Near space passive positioning method and system based on low earth orbit satellite

Abstract

The invention belongs to but not limited to the technical field of passive positioning, and particularly relates to a near space passive positioning method and system based on a low-orbit satellite, and the method comprises the steps: S1, satellite orbit design: carrying out the orbit design of a satellite formation for a target area; s2, acquiring a required observation value, acquiring a time difference and a frequency difference between two paths of signals by using a second-order cross-ambiguity function, and estimating an arrival angle of an incoming wave signal by using a multiple signal classification algorithm; s3, joint positioning: establishing an equation set about the position of the radiation source by using the geometrical relationship between the satellite and the position of the radiation source and the definitions of TDOA and FDOA; s4, solving an estimated value of the position of the radiation source; and S5, the formation satellites solve the positions of the radiation sources through the simultaneous positioning equation set and then send the positions to the ground station, and the ground station reprocesses the received possible positions of the radiation sources.

Description

Technical Field

[0001] The present invention belongs to but is not limited to the field of passive positioning technology, and in particular relates to a near-space passive positioning method and system based on a low-orbit satellite. Background Art

[0002] The positioning of the target can be divided into two methods: passive positioning and active positioning, depending on whether the positioning target emits radiation signals. Active positioning technology refers to the use of active equipment such as radar, laser, sonar, etc. to locate the target. It has the advantages of all-weather and high precision. Passive positioning technology is to receive the signal emitted by the interference source, analyze and process the signal to obtain the location information of the interference source. At present, global navigation and positioning systems, such as GPS, GLONASS, Beidou, etc., are mainly active positioning systems. Although active positioning systems have advantages in accuracy and stability, they also have some disadvantages. For example, signals need to be transmitted during positioning, which means that additional hardware equipment is required, which will increase the cost and maintenance difficulty of the system, and the transmitted signals may be subject to electronic interference, thereby reducing positioning accuracy or causing positioning failure.

[0003] During the positioning process, the passive positioning system has the advantages of strong concealment and strong anti-interference ability because the satellite itself does not emit electromagnetic wave signals. Common passive positioning systems can be divided into multiple types, including positioning methods based on the direction of arrival angle (AOA), arrival time (TOA), arrival time difference (TDOA), and arrival frequency difference (FDOA). The AOA positioning system is simple, but the accuracy is limited; the multi-station TOA positioning system requires strict synchronization of the radiation source and the observation station time, but in practical applications, the location of the radiation source is usually unknown, so it is difficult to achieve time synchronization; TDOA positioning usually adopts three-station joint positioning, which only requires strict synchronization of the time between the observation stations, but requires the solution of the earth's surface equations; FDOA is usually combined with TDOA for positioning, and the classic dual-star time-frequency difference joint positioning also requires the target to be constrained on the earth's surface. There are many different positioning methods, each with its own characteristics and applicable application scenarios.

[0004] In view of the above analysis, the technical problems that need to be urgently solved in the existing technology are: the current system is difficult to receive low-power transmission signals, so it is impossible to effectively locate the target. In addition, many passive positioning methods require the simultaneous calculation of the earth's surface equations, which may lead to large positioning errors in practical applications, especially in the high-precision positioning and identification and tracking of targets equipped with radio equipment in critical spaces. Summary of the invention

[0005] In view of the problems existing in the prior art, the present invention provides a near-space passive positioning method and system based on low-orbit satellites.

[0006] The present invention is implemented as follows: a near-space passive positioning method based on a low-orbit satellite comprises:

[0007] S1, satellite orbit design, orbit design of low-orbit satellite formation for the target area.

[0008] S2, obtain the required observation values, use the second-order mutual ambiguity function to obtain the time difference and frequency difference between the two signals, and use the multiple signal classification algorithm to estimate the arrival angle of the incoming signal.

[0009] S3, joint positioning, uses the geometric relationship between the satellite and the radiation source position and the definitions of TDOA and FDOA to establish a set of equations about the radiation source position.

[0010] S4, solve the estimated value of the radiation source position.

[0011] S5, the formation satellites solve the radiation source positions through the simultaneous positioning equations and send them back to the ground station, and the ground station reprocesses the possible positions of the multiple radiation sources received.

[0012] Furthermore, S1 specifically includes:

[0013] 1. Orbit type selection: The orbital radius of a circular orbit remains unchanged, the position of the satellite changes relatively evenly, the perturbation effect is relatively simple, and the orbit is relatively stable. A circular orbit is selected for satellite formation.

[0014] 2. Determination of orbital parameters: Use the six orbital numbers to characterize the satellite's orbital shape, position, and motion properties. By calculating and analyzing the six orbital numbers, the satellite's future position and motion trajectory can be predicted. The six orbital numbers include the orbital semi-major axis a, eccentricity e, orbital inclination i, perigee argument ω, ascending node right ascension Ω, and true anomaly The orbital semi-major axis and orbital eccentricity determine the size and shape of the orbit, the orbital inclination and the right ascension of the ascending node determine the relative position of the orbital plane and the earth, the perigee argument and true anomaly angle determine the satellite's position change over time, the satellite coverage range is determined by the antenna coverage semi-cone angle θ, r is the coverage radius, and satellite simulation software is used to simulate satellite orbital parameters to ensure that the satellite can cover the target area.

[0015] 3. Satellite formation design: Design the relative geometric configuration of satellites according to mission requirements, coordinate orbit types and parameters for satellite formation, and ensure the best coverage of a specific area by ensuring that the target area is located inside the sub-satellite point of the satellite formation, so that multiple satellites can cover the target area at the same time, and the satellites can receive signals from radiation sources located in the target area. Both parallelogram formations and star formations can meet the requirements of the positioning system for coverage of the target area. If the number of formations is greater than 3 satellites, select star formations or parallelogram formations to fully cover the target area.

[0016] Furthermore, S2 specifically includes:

[0017] Joint estimation of time-frequency difference through mutual fuzzy function:

[0018] The time difference and frequency difference are measured through the mutual ambiguity function, and the two are processed simultaneously to avoid mutual influence, providing parameters for subsequent positioning solution.

[0019] After the satellite receives the signal, it needs to pre-process the signal to facilitate subsequent operations, such as adjusting the signal strength to compensate for signal attenuation, removing signal interference and noise, improving signal quality, converting analog signals into digital signals, etc.

[0020] Assume that signals x1(t) and x2(t) are signals from the same radiation source received by the satellite.

[0021]

[0022] Δf represents the frequency difference between the signals, Δt represents the time delay of the signal, n1(t) and n2(t) represent the signal noise, and A represents the amplitude difference of the received signal.

[0023] The second-order mutual ambiguity function is a two-dimensional correlation function of time difference and frequency difference. The second-order mutual ambiguity function A(f, τ) is calculated for the received signals x1(t) and x2(t). By solving the peak value of |A(f, τ)|, the time difference and frequency difference of the signal can be obtained.

[0024] The second-order mutual ambiguity function of signals x1(t) and x2(t) is:

[0025]

[0026] Assuming s(t), n1(t), n2(t) are independent of each other, when T tends to infinity:

[0027]

[0028] in: search By measuring the peak value of the signal, we can get the TDOA and FDOA of the signal.

[0029] AOA Estimates:

[0030] 1. Calculate the covariance of the received signal

[0031] Assume that the system has M receiving antennas and N transmitting antennas, and the received signal is:

[0032]

[0033] s n(t) represents the nth source signal, represents the phase difference received by adjacent antennas, d represents the length between receiving antennas, λ represents the wavelength of the radiation source signal, and w m (t) represents the noise signal, θ n represents the direction angle of the nth signal, and the received signal can be expressed as:

[0034]

[0035]

[0036] That is, X=AS+W.

[0037] The covariance matrix can be expressed as:

[0038] R xx =E[XX H ]=E[ASS H A]+E[WW H ]=AR SS A H +σ 2 I

[0039] Among them, AR SS A H is the signal term, σ 2 I is the noise term.

[0040] 2. Perform eigenvalue decomposition on the covariance matrix, extract eigenvalues ​​and eigenvectors, sort the eigenvalue vectors according to the descending order of the eigenvalues, and construct the noise space matrix as follows:

[0041] Q N =[q M+1 q M+2 ... q N ]

[0042] 3. Using the orthogonal characteristics of the “noise subspace” and the “signal subspace”, the arrival angle θ of any signal i , establish the spatial spectrum function:

[0043]

[0044] 4. Search for the peak of the spatial spectrum function, and the angle corresponding to the maximum value is the AOA estimation value.

[0045] Furthermore, S3 specifically includes:

[0046] S31, multi-satellite time difference positioning:

[0047] Since there is a time difference TDOA between the signals arriving at the two satellites, TDOA can be used to form an equal time difference hyperbolic surface and obtain a positioning equation. Multiple time differences can obtain multiple positioning equations, and then a positioning equation group can be obtained.

[0048] Assume the spatial position of the satellite formation is S i =(x i ,y i ,z i ) T ,i=1,2,…,N,speed is V i =(v xi ,v yi ,v zi ) T ,i=1,2,…,N, where N is the number of satellites in the satellite formation. For the multi-satellite time difference positioning method mentioned in this article, the number of satellites N≥4, and the default coordinates of the main satellite are S1=(x1,y1,z1) T , the remaining satellites are secondary satellites, P = (x, y, z) T is the true position of the radiation source.

[0049] r i represents the distance between the target signal and the i-th satellite, Δr i represents the distance difference between the radiation source and the host star and the i-th satellite, Δt i represents the time difference between the radiation source to the main star and to the i-th satellite, c is the speed of light, then

[0050]

[0051] △r i =r i -r1

[0052] Then we can get the multi-satellite time difference positioning equation:

[0053]

[0054] The three-dimensional position coordinates of the radiation source are obtained by solving the positioning equations.

[0055] S32, TDOA-FDOA-AOA joint positioning:

[0056] 1. TDOA positioning equation

[0057] Let S1=(x1,y1,z1) T is the main star position, and its velocity is V1=(v x1 ,v y1 ,v z1 ) T ; S2=(x2,y2,z2) Tis the position of the secondary star, and its speed is V2=(v x2 ,v y2 ,v z2 ) T ; P = (x, y, z) T is the true position of the radiation source,

[0058] r i represents the distance between the radiation source and the i-th station, Δr represents the distance difference between the radiation source and the primary star and the secondary star, Δt represents the time difference between the radiation source and the primary star and the secondary star, c is the speed of light,

[0059]

[0060] Δr=r2-r1=c·Δt

[0061] Then the TDOA positioning equation can be obtained:

[0062]

[0063] 2. FDOA positioning equation

[0064] Due to the movement of the satellites, the carrier frequencies of the signals reaching the two satellites will produce Doppler frequency shift, resulting in a difference FDOA in the frequencies received by the two satellites. FDOA can be used to form an equal frequency difference surface and obtain a positioning equation.

[0065] The arrival frequency difference between the two satellites is Δf, where f is the frequency of the radiation source signal and λ is the wavelength of the radiation source signal. is the radial velocity difference between the two satellites and the radiation source, is the actual radial velocity between the ith satellite and the radiation source when there is no error.

[0066]

[0067]

[0068]

[0069] From the above formula we can get:

[0070]

[0071] The FDOA positioning equation is obtained as:

[0072]

[0073] 3.AOA positioning equation

[0074] The geometric relationship between the interferometer composed of two antenna arrays on the main satellite and the radiation source is as follows: Figure 8As shown, β represents the incoming wave direction angle of the radiation source, and α represents the attitude angle of the two baselines.

[0075] The AOA positioning equation can be obtained from the geometric relationship:

[0076] (y-y1)-(x-x1)·tanβ=0

[0077] S33, constructing a positioning equation group based on the arrival time difference TDOA, the arrival frequency difference FDOA, and the incoming wave direction angle β;

[0078] The above parameters are time-calibrated and the positioning equations are obtained together.

[0079]

[0080] Two satellites can obtain three positioning equations, and a satellite formation of N satellites (N≥4) can form positioning equations, which include The time difference positioning equation, The frequency difference positioning equations and N arrival angle positioning equations can be solved by combining multiple positioning methods, or a positioning method with higher accuracy can be selected based on the actual hardware measurement error.

[0081] The three-dimensional position coordinates of the radiation source are obtained by solving the positioning equations.

[0082] Another object of the present invention is to provide a low-orbit satellite-based near-space passive positioning system for implementing the low-orbit satellite-based near-space passive positioning method, comprising:

[0083] Satellite orbit design module, which designs the orbit of satellite formation for the target area.

[0084] The required observation value acquisition module uses the second-order mutual ambiguity function to obtain the time difference and frequency difference between the two signals, and uses the multiple signal classification algorithm to estimate the arrival angle of the incoming signal.

[0085] The joint positioning module uses the geometric relationship between the satellite and the radiation source position and the definitions of TDOA and FDOA to establish a set of equations about the radiation source position.

[0086] The estimated value solving module solves the estimated value of the radiation source position.

[0087] In the reprocessing module, the formation satellites solve the positions of the radiation sources through the simultaneous positioning equations and send them back to the ground station. The ground station reprocesses the possible positions of the multiple radiation sources received.

[0088] Another object of the present invention is to provide a computer device, which includes a memory and a processor, wherein the memory stores a computer program, and when the computer program is executed by the processor, the processor executes the steps of the near-space passive positioning method based on low-orbit satellites.

[0089] Another object of the present invention is to provide a computer-readable storage medium storing a computer program. When the computer program is executed by a processor, the processor executes the steps of the near-space passive positioning method based on low-orbit satellites.

[0090] Another object of the present invention is to provide an information data processing terminal, which includes the near-space passive positioning system based on low-orbit satellites.

[0091] In combination with the above technical solutions and the technical problems solved, the advantages and positive effects of the technical solutions to be protected by the present invention are as follows:

[0092] First, positioning is performed through low-orbit satellite formations, with various positioning methods and flexible positioning areas. Select appropriate satellite formations, such as square and star formations, combine multiple satellites and multiple passive positioning methods, and selectively use positioning methods with high accuracy and suitable for the current background and conditions, overcoming the limitations of traditional single methods. Compared with medium-orbit and high-orbit satellites, low-orbit satellites are more likely to receive low-power signals, improving the positioning accuracy of weak signals.

[0093] After the satellite formation sends the positioning results back to the ground station, the ground station evaluates the error and reliability of each positioning result and reintegrates the positioning data from different satellites, thereby improving the reliability and accuracy of positioning and making it more suitable for the complex environment of near space.

[0094] Compared with the previous three-star time difference positioning and TDOA / FDOA joint positioning, the multi-star time difference positioning and TDOA-FDOA-AOA joint passive positioning method mentioned in this technical method can combine the three measurement technologies of TDOA, FDOA and AOA to suppress the positioning measurement error, and do not require the constraints of the earth's surface, thereby realizing the identification and tracking of targets carrying radio equipment in the earth's near-space.

[0095] Second, as auxiliary evidence of the inventiveness of the claims of the present invention, it is also reflected in the following important aspects:

[0096] (1) The expected benefits and commercial value of the technical solution of the present invention after transformation are:

[0097] The present invention combines passive positioning technology with a low-orbit satellite formation, and then processes the positioning results through a ground station. It is expected to significantly improve the accuracy and reliability of positioning services. This technology can be widely used in transportation, logistics, unmanned driving and other fields to meet the market demand for high-precision positioning services. Passive positioning does not require the transmission of signals, which reduces satellite operating costs, making the popularization and commercialization of services more feasible.

[0098] (2) The technical solution of the present invention overcomes technical prejudice:

[0099] Traditional positioning technology often believes that only medium-orbit or high-orbit satellites have a large coverage area and can provide stable positioning services, and the potential of low-orbit satellites in passive positioning is underestimated. The technical solution of the present invention shows that low-orbit satellites, due to their low orbital altitude and high flight speed, can also provide high-precision and high-reliability services through the application of satellite formations in passive positioning systems, breaking the technical prejudice. BRIEF DESCRIPTION OF THE DRAWINGS

[0100] Figure 1 is a general flow chart of passive positioning provided by an embodiment of the present invention;

[0101] Figure 2 is a satellite orbit design flow chart provided by an embodiment of the present invention;

[0102] Figure 3 Schematic diagram of six satellite orbit numbers provided by an embodiment of the present invention;

[0103] Figure 4 is a schematic diagram of satellite antenna coverage provided by an embodiment of the present invention;

[0104] Figure 5 is a TDOA / FDOA joint estimation flow chart provided by an embodiment of the present invention;

[0105] Figure 6 is a flow chart of the estimation of the direction angle of incoming waves provided by an embodiment of the present invention;

[0106] Figure 7 is a schematic diagram of a positioning process provided by an embodiment of the present invention;

[0107] Figure 8 is a geometric diagram of the incoming wave direction angle provided by an embodiment of the present invention;

[0108] Fig. 9 is a schematic diagram of the positioning accuracy distribution of a triangle formation provided by an embodiment of the present invention;

[0109] Fig.10 is a schematic diagram of the distribution of positioning accuracy of a star formation provided by an embodiment of the present invention;

[0110] Fig.11 is a schematic diagram of the distribution of positioning accuracy of a square formation provided by an embodiment of the present invention;

[0111] Fig.12 is a schematic diagram of the positioning accuracy distribution of a parallelogram formation provided by an embodiment of the present invention;

[0112] Fig.13 It is a structural diagram of a near-space passive positioning system based on a low-orbit satellite provided in an embodiment of the present invention.

[0113] Fig.14 is the CRLB of the star formation with different time difference measurement errors

[0114] Fig.15 is the CRLB of the measurement error of different frequency differences of the star formation

[0115] Fig.16 is the CRLB of the measurement error of the star formation at different angles DETAILED DESCRIPTION

[0116] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0117] like Figure 1 As shown, the near-space passive positioning method based on low-orbit satellites provided in an embodiment of the present invention includes:

[0118] S1. Satellite orbit design:

[0119] 1. Track type selection

[0120] There are various types of orbits, including circular orbits, geosynchronous orbits, and elliptical orbits.

[0121] Geosynchronous orbits are divided into geostationary orbits, inclined geosynchronous orbits, and polar synchronous orbits. Geostationary orbits, that is, the satellite orbit plane has an inclination of zero degrees, and it runs over the equator, 35,786 km from the earth's surface, covering a large area, and the running direction and period are the same as the earth. Geostationary orbit satellites are often used for communication, navigation, etc. Inclined geosynchronous orbits are geosynchronous orbits with an inclination angle that is not zero. Its subsatellite point spans the northern and southern hemispheres and can cover areas with higher latitudes. Polar synchronous orbits (sun-synchronous orbits), that is, the relative position of the satellite orbit plane and the sun remains unchanged, and the orbital inclination is close to 90 degrees. The coverage can reach the north and south poles, and is usually used for meteorological satellites and high-latitude communication satellites.

[0122] Elliptical orbits include lightning orbits, high elliptical orbits, and critical inclination orbits. A lightning orbit is a large elliptical critical inclination orbit, where the satellite on the orbit stays longer in the hemisphere it serves, while running faster in the other hemisphere, providing communication and remote sensing services for the hemisphere it serves; a high elliptical orbit has a lower perigee and an extremely high apogee, with the apogee altitude much greater than 36,000 km, and can cover the area below the apogee for more than 12 hours; a critical inclination orbit is an orbit with an inclination of 63.4°, and natural perturbations will not cause the major axis of the ellipse to rotate in the orbital plane. It is also called a frozen orbit.

[0123] Due to the irregular shape of the earth, and the higher average density and uneven mass in some areas, these factors will lead to an uneven gravitational field around the earth. Satellites at different points in orbit will receive different forces. Other perturbations include the aerodynamic force of the upper atmosphere, the gravity of the sun and the moon, and the pressure of sunlight. Under the long-term action of these perturbations, the satellite orbital period, eccentricity, and inclination continue to change. The perturbations on elliptical orbits are more complex and have a greater impact on the orbit. The orbital radius of a circular orbit remains unchanged, the position of the satellite changes relatively evenly, the perturbations are simpler, and the orbit is more stable. Therefore, a circular orbit is chosen for satellite formation.

[0124] 2. Determination of orbital parameters

[0125] The six orbital numbers can directly reflect the basic characteristics of the orbit. Artificial satellites usually use the six orbital numbers to characterize the shape, position and motion of the satellite orbit. By calculating and analyzing the six orbital numbers, the future position and motion trajectory of the satellite can be accurately predicted. The six orbital numbers include the orbital semi-major axis a, the eccentricity e, the orbital inclination i, the perigee angle ω, the ascending node right ascension Ω and the true anomaly angle The orbital semi-major axis and orbital eccentricity determine the size and shape of the orbit, the orbital inclination and the right ascension of the ascending node determine the relative position of the orbital plane and the earth, the perigee argument and true anomaly angle determine the satellite's position change over time, the satellite coverage range is determined by the antenna coverage semi-cone angle θ, r is the coverage radius, and satellite simulation software is used to simulate satellite orbital parameters to ensure that the satellite can cover the target area.

[0126] 3. Satellite formation design

[0127] Passive positioning usually requires multiple satellites to work together, so satellite formation is necessary. The relative geometric configuration of the satellites is designed according to the mission requirements. Common configurations include: linear, star, triangle, parallelogram, etc., and the orbit type and parameters are coordinated to form a satellite formation. In order to ensure the best coverage of a specific area, it is necessary to ensure that the target area is located inside the sub-satellite point of the satellite formation, so that multiple satellites can cover the target area at the same time, and the satellites can receive signals from the radiation source located in the target area.

[0128] By simulating and analyzing the coverage performance of the satellite formations mentioned above, it is found that the coverage of the target area by both the parallelogram formation and the star formation can meet the requirements of the positioning system.

[0129] In order to achieve positioning and improve positioning accuracy, the number of satellites in the formation should be greater than 3. Through the coverage performance analysis of common formation configurations, choosing a star formation or a parallelogram formation can fully cover the target area.

[0130] S2 obtains the required observations:

[0131] Since the satellites are moving and the distances between the satellite formation and the radiation source are different, there are time differences and frequency differences in the signals from the same radiation source received by the satellites. Each satellite receives the signal from the radiation source respectively. After preprocessing the signal such as noise reduction filtering, the satellite transmits its own signal to other satellites through the intersatellite link, and defaults to itself as the master satellite to estimate the TDOA, FDOA, and AOA parameters.

[0132] Before parameter estimation, it is necessary to ensure that the time of the primary satellite and the secondary satellite is highly synchronized. Each satellite is equipped with a GPS receiver. The atomic clock on the GPS satellite provides an accurate time reference. The satellite receives the time signal sent by the GPS satellite and corrects its own time to keep it consistent with the time of the GPS system, thereby achieving satellite formation time synchronization.

[0133] 1. Joint estimation of time-frequency difference through mutual fuzzy function

[0134] The time difference and frequency difference are measured through the mutual ambiguity function, and the two are processed simultaneously to avoid mutual influence, providing parameters for subsequent positioning solution.

[0135] After the satellite receives the signal, it needs to pre-process the signal to facilitate subsequent operations. Adjust the signal strength to compensate for signal attenuation; remove signal interference and noise, improve signal quality, convert analog signals into digital signals, etc.

[0136] Assume that signals x1(t) and x2(t) are signals from the same radiation source received by the satellite.

[0137]

[0138] Δf represents the frequency difference between the signals, Δt represents the time delay of the signal, n1(t) and n2(t) represent the signal noise, and A represents the amplitude difference of the received signal.

[0139] The second-order mutual ambiguity function is a two-dimensional correlation function of time difference and frequency difference. The second-order mutual ambiguity function A(f, τ) is calculated for the received signals x1(t) and x2(t). By solving the peak value of |A(f, τ)|, the time difference and frequency difference of the signal can be obtained.

[0140] The second-order mutual ambiguity function of signals x1(t) and x2(t) is:

[0141]

[0142] Assuming s(t), n1(t), n2(t) are independent of each other, when T tends to infinity:

[0143]

[0144] in: search By measuring the peak value of the signal, we can get the TDOA and FDOA of the signal.

[0145] 2. AOA estimation

[0146] 1. Calculate the covariance of the received signal

[0147] Assume that the system has M receiving antennas and N transmitting antennas, and the received signal is:

[0148]

[0149] s n (t) represents the nth source signal, represents the phase difference received by adjacent antennas, d represents the length between receiving antennas, λ represents the wavelength of the radiation source signal, and w m (t) represents the noise signal, θ n represents the direction angle of the nth signal, and the received signal can be expressed as:

[0150]

[0151]

[0152] That is, X=AS+W.

[0153] The covariance matrix can be expressed as:

[0154] R xx =E[XX H ]=E[ASS H A]+E[WW H ]=AR SS A H +σ 2 I

[0155] Among them, AR SS A H is the signal term, σ 2 I is the noise term.

[0156] 2. Perform eigenvalue decomposition on the covariance matrix, extract eigenvalues ​​and eigenvectors, sort the eigenvalue vectors according to the descending order of the eigenvalues, and construct the noise space matrix as follows:

[0157] Q N =[q M+1 q M+2 ... q N ]

[0158] 3. Using the orthogonal characteristics of the “noise subspace” and the “signal subspace”, the arrival angle θ of any signal i , establish the spatial spectrum function:

[0159]

[0160] 4. Search for the peak of the spatial spectrum function, and the angle corresponding to the maximum value is the AOA estimation value.

[0161] S3. Joint positioning:

[0162] S31 multi-satellite time difference positioning

[0163] Since there is a time difference TDOA between the signals arriving at the two satellites, TDOA can be used to form an equal time difference hyperbolic surface and obtain a positioning equation. Multiple time differences can obtain multiple positioning equations, and then a positioning equation group can be obtained.

[0164] Assume the spatial position of the satellite formation is S i =(x i ,y i ,z i ) T ,i=1,2,…,N,speed is V i =(v xi ,v yi ,v zi ) T ,i=1,2,…,N, where N is the number of satellites in the satellite formation. For the multi-satellite time difference positioning method mentioned in this article, the number of satellites N≥4, and the default coordinates of the main satellite are S1=(x1,y1,z1) T , the remaining satellites are secondary satellites, P = (x, y, z) T is the true position of the radiation source.

[0165] r i represents the distance between the target signal and the i-th satellite, Δr i represents the distance difference between the radiation source and the host star and the i-th satellite, Δti represents the time difference between the radiation source to the main star and to the i-th satellite, c is the speed of light, then

[0166]

[0167] Δr i =r i -r1

[0168] Then we can get the multi-satellite time difference positioning equation:

[0169]

[0170] The three-dimensional position coordinates of the radiation source are obtained by solving the positioning equations.

[0171] S32TDOA-FDOA-AOA joint positioning

[0172] 1. TDOA positioning equation

[0173] Let S1=(x1,y1,z1) T is the main star position, and its velocity is V1=(v x1 ,v y1 ,v z1 ) T ; S2=(x2,y2,z2) T is the position of the secondary star, and its speed is V2=(v x2 ,v y2 ,v z2 ) T ; P = (x, y, z) T is the true position of the radiation source,

[0174] r i represents the distance between the radiation source and the i-th station, Δr represents the distance difference between the radiation source and the primary star and the secondary star, Δt represents the time difference between the radiation source and the primary star and the secondary star, c is the speed of light,

[0175]

[0176] Δr=r2-r1=c·Δt

[0177] Then the TDOA positioning equation can be obtained:

[0178]

[0179] 2. FDOA positioning equation

[0180] Due to the movement of the satellites, the carrier frequencies of the signals reaching the two satellites will produce Doppler frequency shift, resulting in a difference FDOA in the frequencies received by the two satellites. FDOA can be used to form an equal frequency difference surface and obtain a positioning equation.

[0181] The arrival frequency difference between the two satellites is Δf, where f is the frequency of the radiation source signal and λ is the wavelength of the radiation source signal. is the radial velocity difference between the two satellites and the radiation source, is the actual radial velocity between the ith satellite and the radiation source when there is no error.

[0182]

[0183]

[0184]

[0185] From the above formula we can get:

[0186]

[0187] The FDOA positioning equation is obtained as:

[0188]

[0189] 3.AOA positioning equation

[0190] The geometric relationship between the interferometer composed of two antenna arrays on the main satellite and the radiation source is as follows: Figure 8 As shown, β represents the incoming wave direction angle of the radiation source, and α represents the attitude angle of the two baselines.

[0191] The AOA positioning equation can be obtained from the geometric relationship:

[0192] (y-y1)-(x-x1)·tanβ=0

[0193] S33. Construct positioning equations based on arrival time difference TDOA, arrival frequency difference FDOA, and incoming wave direction angle β

[0194] The above parameters are time-calibrated and the three positioning equations are combined to obtain the positioning equation group.

[0195]

[0196] Two satellites can obtain three positioning equations, and a satellite formation of N satellites (N≥4) can form positioning equations, which include The time difference positioning equation, The frequency difference positioning equations and N arrival angle positioning equations can be solved by combining multiple positioning methods, or a positioning method with higher accuracy can be selected based on the actual hardware measurement error.

[0197] The three-dimensional position coordinates of the radiation source are obtained by solving the positioning equations.

[0198] S4 Ground Station Processing

[0199] The formation satellites use the simultaneous positioning equations to solve the radiation source positions and send them back to the ground station, which then reprocesses the possible positions of multiple radiation sources received. The consistency of the data between satellites is checked, the error and reliability of each positioning result is evaluated, and the positioning data from different satellites are re-integrated using weighted average to obtain a comprehensive positioning result.

[0200] like Fig.13 As shown, the near-space passive positioning system based on low-orbit satellites provided in an embodiment of the present invention includes:

[0201] Satellite orbit design module, which designs the orbit of satellite formation for the target area;

[0202] The required observation value acquisition module uses the second-order mutual ambiguity function to obtain the time difference and frequency difference between the two signals, and uses the multiple signal classification algorithm to estimate the arrival angle of the incoming signal;

[0203] The joint positioning module uses the geometric relationship between the satellite and the radiation source position and the definition of TDOA and FDOA to establish a set of equations about the radiation source position;

[0204] An estimated value solving module solves the estimated value of the radiation source position;

[0205] In the reprocessing module, the formation satellites solve the positions of the radiation sources through the simultaneous positioning equations and send them back to the ground station. The ground station reprocesses the possible positions of the multiple radiation sources received.

[0206] An application embodiment of the present invention provides a computer device, which includes a memory and a processor. The memory stores a computer program. When the computer program is executed by the processor, the processor executes the steps of a near-space passive positioning method based on a low-orbit satellite.

[0207] An application embodiment of the present invention provides a computer-readable storage medium storing a computer program. When the computer program is executed by a processor, the processor executes the steps of a near-space passive positioning method based on a low-orbit satellite.

[0208] An application embodiment of the present invention provides an information data processing terminal, which includes a near-space passive positioning system based on a low-orbit satellite.

[0209] 1. Specific application fields or related products of the present invention.

[0210] The present invention can be applied to the aerospace field to improve the positioning accuracy of satellites for near-space aircraft, such as high-altitude drones, airplanes, balloons and other targets carrying radio equipment. Combining multiple satellites and multiple passive positioning methods overcomes the limitations of traditional single positioning methods and adapts to the needs of multiple application scenarios.

[0211] 2. Relevant evidence of the technical effects obtained by the embodiments of the present invention.

[0212] Through simulation analysis, the effects of different satellite formation shapes and measurement errors on positioning accuracy are analyzed in order to select the appropriate satellite formation.

[0213] The simulation conditions are shown in Table 1: Table 1 shows the latitude and longitude coordinates of the satellite formation in four different shapes: triangle, star, square, and parallelogram. The satellite altitude is 800km. The geometric precision factor of the satellite formation is simulated when the satellite position error is 5m and the time difference measurement accuracy is 5ns.

[0214] Table 1 Satellite longitude and latitude in 4 satellite formation modes

[0215]

[0216]

[0217] The simulation results are as follows Fig. 9 , Fig.10 , Fig.11 , Fig.12 As shown in the figure, "*" is the satellite position. Under the same measurement parameter conditions, the more satellites there are in the satellite formation, the more equations that can be solved and the higher the positioning accuracy. The triangular formation has the worst positioning longitude. Among them, the positioning accuracy of the star formation is evenly distributed around the satellite position, but the accuracy is worse than that of the square formation and parallelogram formation. On the same positioning accuracy curve, the parallelogram formation has a larger radiation range. When selecting a satellite formation, you can make a comprehensive selection based on coverage and positioning accuracy.

[0218] Replenish:

[0219] The CRLB of the multi-satellite positioning algorithm is simulated under different time difference measurement errors, different frequency measurement errors and different angle measurement errors. The results are as follows: Fig.14 , 15 As shown in ,16, the appropriate passive positioning algorithm can be selected according to the actual hardware measurement situation.

[0220] Taking a four-satellite formation as an example to illustrate the influence of time difference positioning error, frequency difference positioning error and wave arrival angle measurement error on CRLB, the satellite formation is "star", the satellite altitude is 800km, the satellite positions are as written in Table 1, and the satellite flight speeds are V1 = [-2.25km / s-2.15km / s6.59km / s]; V2 = [-2.3km / s-2.18km / s6.55km / s]; V1 = [-2.25km / s-2.25km / s6.53km / s]; V1 = [-2.25km / s-2.15km / s6.59km / s]; the results are as follows Fig.14 , 15 As shown in , 16, in practical applications, the applicable positioning method can be selected by referring to the estimation errors of different time differences, frequency differences, and arrival angles of incoming waves.

[0221] It should be noted that the embodiments of the present invention can be implemented by hardware, software, or a combination of software and hardware. The hardware part can be implemented using dedicated logic; the software part can be stored in a memory and executed by an appropriate instruction execution system, such as a microprocessor or dedicated design hardware. It can be understood by a person of ordinary skill in the art that the above-mentioned devices and methods can be implemented using computer executable instructions and / or contained in a processor control code, such as a carrier medium such as a disk, CD or DVD-ROM, a programmable memory such as a read-only memory (firmware), or a data carrier such as an optical or electronic signal carrier. Such code is provided on the carrier medium. The device and its modules of the present invention can be implemented by hardware circuits such as very large-scale integrated circuits or gate arrays, semiconductors such as logic chips, transistors, etc., or programmable hardware devices such as field programmable gate arrays, programmable logic devices, etc., can also be implemented by software executed by various types of processors, and can also be implemented by a combination of the above-mentioned hardware circuits and software, such as firmware.

[0222] The above description is only a specific implementation mode of the present invention, but the protection scope of the present invention is not limited thereto. Any modifications, equivalent substitutions and improvements made by any technician familiar with the technical field within the technical scope disclosed by the present invention and within the spirit and principle of the present invention should be covered by the protection scope of the present invention.

Claims

1. A near-space passive positioning method based on low-orbit satellites, characterized in that: include: S1, satellite orbit design, orbit design of satellite formation for target area; S2, obtain the required observation values, use the second-order mutual ambiguity function to obtain the time difference and frequency difference between the two signals, and use the multiple signal classification algorithm to estimate the arrival angle of the incoming signal; S3, joint positioning, uses the geometric relationship between the satellite and the radiation source position and the definition of TDOA and FDOA to establish a set of equations about the radiation source position; S4, solving the estimated value of the radiation source position; S5, the formation satellites solve the radiation source positions through the simultaneous positioning equations and send them back to the ground station, and the ground station reprocesses the possible positions of the multiple radiation sources received.

2. The near-space passive positioning method based on low-orbit satellite according to claim 1, characterized in that: S1 specifically includes: Orbit type selection: The orbit radius of a circular orbit remains unchanged, the position of the satellite changes relatively evenly, the perturbation effect is relatively simple, and the orbit is relatively stable. A circular orbit is selected for satellite formation; Orbital parameter determination: The six orbital numbers are used to characterize the satellite orbital shape, position and motion properties. By calculating and analyzing the six orbital numbers, the future position and motion trajectory of the satellite are predicted; the six orbital numbers include the orbital semi-major axis a, eccentricity e, orbital inclination i, perigee argument ω, ascending node right ascension Ω and true anomaly angle The orbit semi-major axis and orbit eccentricity determine the size and shape of the orbit, the orbit inclination and the right ascension of the ascending node determine the relative position of the orbit plane and the earth, the perigee argument and true anomaly angle determine the position change of the satellite over time, the satellite coverage range is determined by the antenna coverage semi-cone angle θ, r is the coverage radius, and satellite simulation software is used to simulate satellite orbit parameters to ensure that the satellite can cover the target area; Satellite formation design: Design the relative geometric configuration of satellites according to mission requirements, coordinate orbit types and parameters to form satellites, and ensure the best coverage of a specific area and the target area is located inside the sub-satellite point of the satellite formation so that multiple satellites can cover the target area at the same time. The satellites can receive signals from radiation sources in the target area. The coverage of the target area by both parallelogram formations and star formations meets the requirements of the positioning system. If the number of formations is greater than 3 satellites, select star formations or parallelogram formations to fully cover the target area.

3. The near-space passive positioning method based on low-orbit satellite according to claim 1, characterized in that: S2 specifically includes: Joint estimation of time-frequency difference through mutual fuzzy function: The time difference and frequency difference are measured through the mutual ambiguity function, and the two are processed simultaneously to avoid mutual influence and provide parameters for subsequent positioning solution; After the satellite receives the signal, it needs to pre-process the signal to facilitate subsequent operations; adjust the signal strength to compensate for signal attenuation; remove signal interference and noise, improve signal quality, and convert analog signals into digital signals; Assume that signals x1(t) and x2(t) are signals from the same radiation source received by the satellite. Δf represents the frequency difference between the signals, Δt represents the delay of the signal, n1(t) and n2(t) represent the signal noise, and A represents the amplitude difference of the received signal; The second-order mutual ambiguity function is a two-dimensional correlation function of the time difference and the frequency difference. The second-order mutual ambiguity function A(f, τ) is calculated for the received signals x1(t) and x2(t). By solving the peak value of |A(f, τ)|, the time difference and frequency difference of the signal are obtained. The second-order mutual ambiguity function of signals x1(t) and x2(t) is: Assuming s(t), n1(t), n2(t) are independent of each other, when T tends to infinity: in: search The peak value of the signal is obtained by measuring the TDOA and FDOA of the signal. AOA Estimates:

1. Calculate the covariance of the received signal Assume that the system has M receiving antennas and N transmitting antennas, and the received signal is: s n (t) represents the nth source signal, represents the phase difference received by adjacent antennas, d represents the length between receiving antennas, λ represents the wavelength of the radiation source signal, and w m (t) represents the noise signal, θ n represents the direction angle of the nth signal, and the received signal can be expressed as: That is, X = AS + W; The covariance matrix can be expressed as: R xx =E[XX H ]=E[ASS H A]+E[WW H ]=AR SS A H +σ 2 I Among them, AR SS A H is the signal term, σ 2 I is the noise term; 2. Perform eigenvalue decomposition on the covariance matrix, extract eigenvalues ​​and eigenvectors, sort the eigenvalue vectors according to the descending order of the eigenvalues, and construct the noise space matrix as follows: Q N =[q M+1 q M+2 ...q N ] 3. Using the orthogonal characteristics of "noise subspace" and "signal subspace", the arrival angle θ of any signal i , establish the spatial spectrum function:

4. Search for the peak of the spatial spectrum function, and the angle corresponding to the maximum value is the AOA estimation value.

4. The near-space passive positioning method based on low-orbit satellite according to claim 1, characterized in that: S3 specifically includes: S31, multi-satellite time difference positioning: Since there is a difference TDOA in the time when the signal arrives at the two satellites, TDOA is used to form an equal time difference hyperboloid to obtain a positioning equation. Multiple time differences can be used to obtain multiple positioning equations, and then a positioning equation group is obtained. Assume the spatial position of the satellite formation is S i =(x i ,y i ,z i ) T ,i=1,2,…,N,speed is V i =(v xi ,v yi ,v zi ) T ,i=1,2,…,N, where N is the number of satellites in the satellite formation; for the multi-satellite time difference positioning method mentioned in this paper, the number of satellites N≥4, and the coordinates of the main satellite are S1=(x1,y1,z1) T , the remaining satellites are secondary satellites, P = (x, y, z) T is the true position of the radiation source; r i represents the distance between the target signal and the i-th satellite, Δr i represents the distance difference between the radiation source and the host star and the i-th satellite, Δt i represents the time difference between the radiation source to the main star and to the i-th satellite, c is the speed of light, then Δr i =r i -r1 Then we can get the multi-satellite time difference positioning equation: The three-dimensional position coordinates of the radiation source are obtained by solving the positioning equations; S32, TDOA-FDOA-AOA joint positioning:

1. TDOA positioning equation Let S1=(x1,y1,z1) T is the main star position, and its velocity is V1=(v x1 ,v y1 ,v z1 ) T ; S2=(x2,y2,z2) T is the position of the secondary star, and its speed is V2=(v x2 ,v y2 ,v z2 ) T ; P = (x, y, z) T is the true position of the radiation source, r i represents the distance between the radiation source and the i-th station, Δr represents the distance difference between the radiation source and the primary star and the secondary star, Δt represents the time difference between the radiation source and the primary star and the secondary star, c is the speed of light, Δr=r2-r1=c·Δt Then the TDOA positioning equation can be obtained:

2. FDOA positioning equation Due to the movement of the satellite, the carrier frequency of the signal reaching the two satellites will produce Doppler frequency shift, so that there is a difference FDOA in the frequencies received by the two satellites. Using FDOA, an equal frequency difference surface is formed to obtain a positioning equation. The arrival frequency difference between the two satellites is Δf, where f is the frequency of the radiation source signal and λ is the wavelength of the radiation source signal. is the radial velocity difference between the two satellites and the radiation source, is the actual radial velocity between the ith satellite and the radiation source when there is no error; From the above formula we can get: The FDOA positioning equation is obtained as: 3.AOA positioning equation The geometric relationship between the interferometer composed of two-unit antenna array on the main satellite and the radiation source is shown in Figure 8, where β represents the incoming wave direction angle of the radiation source and α represents the attitude angle of the two baselines. The AOA positioning equation can be obtained from the geometric relationship: (y-y1)-(x-x1)·tanβ=0 S33, constructing a positioning equation group based on the arrival time difference TDOA, the arrival frequency difference FDOA, and the incoming wave direction angle β; The above parameters are time-calibrated and the positioning equations are obtained together; The three-dimensional position coordinates of the radiation source are obtained by solving the positioning equations.

5. A low-orbit satellite-based near-space passive positioning system for implementing the low-orbit satellite-based near-space passive positioning method as claimed in any one of claims 1 to 4, characterized in that: include: Satellite orbit design module, which designs the orbit of satellite formation for the target area; The required observation value acquisition module uses the second-order mutual ambiguity function to obtain the time difference and frequency difference between the two signals, and uses the multiple signal classification algorithm to estimate the arrival angle of the incoming wave signal; The joint positioning module uses the geometric relationship between the satellite and the radiation source position and the definition of TDOA and FDOA to establish a set of equations about the radiation source position; An estimated value solving module solves the estimated value of the radiation source position; In the reprocessing module, the formation satellites solve the positions of the radiation sources through the simultaneous positioning equations and send them back to the ground station. The ground station reprocesses the possible positions of the multiple radiation sources received.

6. A computer device, comprising a memory and a processor, wherein the memory stores a computer program, and when the computer program is executed by the processor, the processor executes the steps of the near-space passive positioning method based on a low-orbit satellite as described in any one of claims 1 to 4.

7. A computer-readable storage medium storing a computer program, which, when executed by a processor, enables the processor to execute the steps of the near-space passive positioning method based on a low-orbit satellite as described in any one of claims 1 to 4.

8. An information data processing terminal, comprising the near-space passive positioning system based on low-orbit satellite as claimed in claim 5.

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