A network optimization method for constructing a multi-node synchronization link of a spaceborne distributed radar

Abstract

The present invention belongs to the technical field of spaceborne distributed radars, and discloses a network optimization method for constructing a multi-node synchronization link of a spaceborne distributed radar. The present invention includes establishing a distributed multi-satellite system, performing phase synchronization, and improving network stability. In view of the problems that the number of distributed radar nodes is large and phase synchronization is required during collaborative work, on the one hand, in the prior art, the more complex the network structure and the longer the link, the more synchronization error accumulation will be; on the other hand, when the satellite moves, it will cause the position of the node to change, or when a certain node is unstable, it may cause the entire network to collapse. Compared with the prior art, the present invention can dynamically evaluate the signal-to-noise ratio and the mutual occlusion situation of multiple satellites, the system can adapt to environmental changes, optimize the connection between radar points, more effectively construct a radar network, and improve the performance of the network.

Description

Technical Field

[0001] The present invention mainly relates to the technical field of spaceborne distributed radars, and particularly to a network optimization method for constructing a multi-node synchronization link of a spaceborne distributed radar. Background Art

[0002] Phase synchronization is a key technology for spaceborne distributed radars. Its essence is that the frequency offset generated by different frequency sources causes phase errors when the echo signal is demodulated at an inaccurate frequency. When phase-synchronizing typical foreign spaceborne distributed InSAR systems such as TanDEM-X, the pulse-alternating synchronization method is mainly adopted, mainly in the form of "one-to-one" synchronization. However, there are few scholars researching on "many-to-many" phase synchronization in the context of multiple satellites. In the research on ground-based distributed radar synchronization, there are more studies on the synchronization of multiple nodes. However, due to the fixed ground position relationship and short distance, there will be problems such as a decrease in signal-to-noise ratio when the distance is far in multiple satellites, and the influence of occlusion generated during the movement of multiple satellites, etc.

[0003] The main goal in multi-satellite synchronization is still to minimize the total error after each transmission in the link and achieve global optimality. However, the methods for constructing the synchronization link network are different in different applications. In the context of spaceborne distributed radars, there are many radar nodes, and the intercept distances between the target and the radars are inconsistent, which will cause phase deviations. Therefore, phase synchronization is required to correct the deviations. However, there will still be residual phase synchronization errors after phase synchronization correction. It is necessary to use the method of network connection to reduce the residual phase synchronization errors to achieve the optimal performance.

[0004] In current research, there are usually three phase synchronization methods, namely the direct forwarding type, the frequency stabilization type, and the phase synchronization type. Among them, in the phase synchronization type, the master-slave synchronization method is a relatively classical phase synchronization method. Each node only needs to perform point-to-point synchronization with the central node. This method has the advantage of a shorter phase synchronization link, so it has been widely used. However, in actual application scenarios, when the central node is damaged, the entire radar system network will collapse and cannot work properly.

[0005] Therefore, in order to overcome the deficiencies of the classical master-slave synchronization method, the prior art has proposed a cyclic round-trip phase synchronization method, which improves the stability of the distributed radar system. However, it is difficult to implement when the distance between radar nodes is too far, and when a node is damaged, the phase synchronization link is too long, and the error accumulation will be more.

[0006] The current phase synchronization still has problems such as the difficulty in selecting reference satellites, the increasing cumulative errors caused by long links, the influence of satellite position changes during operation, and the instability of the network caused by the instability of a certain node. The current phase synchronization methods are still difficult to take these real situations into account simultaneously. Therefore, it is necessary to find a network connection method that minimizes the link cumulative error for improvement. Summary of the Invention

[0007] Regarding the problem that the number of distributed radar nodes is large and phase synchronization is required in collaborative work, on the one hand, the more complex the network structure and the longer the link, the more synchronization error accumulation will be; on the other hand, satellite movement will cause changes in the positions of nodes, or the instability of a certain node may cause the entire network to collapse. The purpose of this invention is to improve the construction efficiency and performance of the radar network and reduce the link error accumulation by proposing a network optimization method for constructing a multi-node synchronization link of spaceborne distributed radars. This method can dynamically evaluate the connection feasibility between radar points and automatically adjust the connection strategy to cope with complex environmental changes.

[0008] To achieve the above object, this invention provides a network optimization method for constructing a multi-node synchronization link of spaceborne distributed radars, including the following steps:

[0009] Step 1: Establish a distributed multi-satellite system: Establish a distributed multi-satellite system composed of N satellites, select the Mth satellite as the master satellite, and each satellite has T phase synchronization horn antennas;

[0010] Step 2: Perform phase synchronization, including the following steps:

[0011] S1: Each satellite in the distributed multi-satellite system sends status messages: Each satellite sends information including its respective position and attitude at the start time, middle time, and end time of the current work task to the master satellite M, and the master satellite M stores the number of phase synchronization horn antennas of each satellite in advance.

[0012] S2: Determine the phase synchronization reference satellite according to the position and attitude information of each satellite obtained in step S1, put all the satellites that need phase synchronization into the set E, and determine the phase synchronization horn antennas that can be connected to each other between two satellites according to the task.

[0013] S3: Judge the satellite phase synchronization configuration, and identify whether the satellite phase synchronization configuration in the distributed multi-satellite system is a direct synchronization satellite or an indirect synchronization satellite;

[0014] S4: The master satellite M determines the phase synchronization pairing satellite of the direct synchronization satellite;

[0015] S5: The master satellite M determines the phase synchronization pairing satellite of the indirect synchronization satellite;

[0016] S6: Perform phase synchronization: The master satellite M sends the phase synchronization pairing results to each satellite, and each satellite transmits the phase synchronization signals according to the phase synchronization pairing results to achieve the phase synchronization of the distributed multi-satellite system.

[0017] Further, it also includes step 3: Network stability improvement, including the following steps:

[0018] S7: When the probability of each node being damaged is independent and the probability of affecting other nodes is independent, put the unconnected line segments that meet the signal-to-noise ratio threshold and occlusion conditions into the set F;

[0019] S8: Define nodes and connections: Sort the nodes according to the number of nodes they are connected to from most to least, and label them respectively as , each node The number of nodes it is connected to is denoted as ;

[0020] S9: Calculate the impact of a single node being damaged: When the node is damaged, the nodes directly connected to it will be affected. For each node , the expected value of the number of invalid nodes caused by its damage is p × the number of affected nodes, where p is the probability of a single node being damaged;

[0021] S10: Calculate the total expected value: The sum of the impacts caused by any node in the network being damaged is the expected value of the entire network being damaged, and the calculation formula is ;

[0022] S11: Add the connections in the set F to the original network to minimize the total expected value.

[0023] Further, in step S2, determining the phase synchronization reference satellite according to the obtained position and attitude information of each satellite includes the following steps:

[0024] T1: Combine the determined phase synchronization horn antennas to judge the signal-to-noise ratio between satellites i in the set E;

[0025] T2: Judge the occlusion relationship between satellites i in the set E;

[0026] T3: Repeat steps T1 and T2. If there are two satellites i in the set E that meet the signal-to-noise ratio threshold and there is no occlusion, it is considered connectable, and all connectable satellites are put into the set D;

[0027] If there are still satellites in the set E, it means that there are satellites that cannot perform phase synchronization, then the master satellite M reports an error and feeds back the set E to the ground;

[0028] T4: Perform the selection of the phase synchronization reference satellite:

[0029] If there is any satellite P and the most satellites i that satisfy the signal-to-noise ratio threshold, and there is no occlusion, that is, satellite P finds the most satellites that can be connected, then satellite P is the phase synchronization reference satellite;

[0030] If there are different satellites that can connect to the same maximum number of satellites i, that is, when finding the most satellites that can be connected, if there are multiple, randomly select one of them as the phase synchronization reference satellite P.

[0031] Further, in step T1, for any two satellites A and B in the set E that need to perform phase synchronization, the signal-to-noise ratio discrimination method includes the following steps:

[0032] K1: Calculate the slant range between satellite A and B , and the calculation expression is , where represents the position of satellite A, represents the position of satellite B;

[0033] K2: Calculate the signal-to-noise ratio between satellite A and B, and the calculation expression is , where represents the transmit peak power of the phase synchronization horn antenna of satellite A, is the transmit gain of the phase synchronization horn antenna of satellite A, is the transmit gain of the phase synchronization horn antenna of satellite B, is the wavelength, is the processing gain, is the Boltzmann constant, is the temperature, is the bandwidth, is the receive noise figure, is the loss, is the phase synchronization signal-to-noise ratio between satellite A and satellite B;

[0034] K3: Perform signal-to-noise ratio judgment, and stipulate the signal-to-noise ratio threshold according to the actual situation ;

[0035] If ≥ , it indicates that satellite A and satellite B satisfy the signal-to-noise ratio threshold;

[0036] If < , it indicates that satellite A and satellite B do not satisfy the signal-to-noise ratio threshold.

[0037] Further, in step T2, for any two satellites A and B in the set E that need to perform phase synchronization, the occlusion discrimination method includes the following steps:

[0038] K4: Calculate satellite K, where k is a positive integer less than N and not equal to A and B, representing different satellites, N represents the total number of satellites, and the calculation expression is , where represents the angle between the line connecting satellite B and satellite A and the line connecting satellite k and satellite A, represents the arccosine operation, represents the modulo operation, is the position of satellite A, is the position of satellite B, is the position of satellite k;

[0039] K5: Perform occlusion judgment:

[0040] If satellite K satisfies or , it means that there is occlusion in the phase synchronization link between satellite A and satellite B;

[0041] If satellite K does not satisfy or , it means that there is no occlusion in the phase synchronization link between satellite A and satellite B;

[0042] Among them, represents the angle between the line connecting satellite B and satellite A and the line connecting satellite k and satellite A, represents the angle between the line connecting satellite A and satellite B and the line connecting satellite k and satellite B, represents the beam width of the synchronization horn antenna, which can be obtained through a distributed multi-satellite system.

[0043] Further, the satellite phase synchronization configuration judgment in step S3 includes the following steps:

[0044] T5: If satellite P and satellite i meet the signal-to-noise ratio threshold and there is no occlusion, the phase synchronization configuration of the i-th satellite is a direct synchronization satellite;

[0045] If satellite P and satellite i do not meet the signal-to-noise ratio threshold or there is occlusion, the phase synchronization configuration of the i-th satellite is an indirect synchronization satellite;

[0046] T6: Repeat step T5 to determine the phase synchronization configuration of all satellites in set D.

[0047] Further, the main satellite M in step S4 determines the phase synchronization pairing satellite of the direct synchronization satellite, including the following steps:

[0048] T7: For the direct synchronization satellite i in set D, phase synchronization can be directly achieved through the communication signal between satellite P and satellite i. Therefore, pair satellite i with satellite P, remove satellite i from set D, and add satellite i to the connected satellite set C1;

[0049] T8: Perform the operation of step T7 on all direct synchronous satellites in set D.

[0050] Furthermore, in step S5, the master satellite M determines the phase synchronization pairing satellites of the indirect synchronous satellites, including the following steps:

[0051] T9: Initialize the positive integer n = 1;

[0052] T10: For the indirectly synchronous satellite i in set D, use the satellite j in the connected satellite set Cn for phase synchronization pairing. Cn is the set that can be confirmed to be connected after n judgments. The specific steps are as follows:

[0053] Q1: For the indirectly synchronous satellite i in set D, use the satellite j in the connected satellite set Cn to perform the selection of phase synchronization horn antennas, signal-to-noise ratio judgment, and occlusion judgment;

[0054] If the satellite P1 in the connected satellite set Cn and the most indirectly synchronous satellite i in set D both meet the signal-to-noise ratio threshold and there is no occlusion, then designate the satellite P1 as the first-level phase synchronization reference satellite. The satellite P1 in the connected satellite set Cn and the satellite i are preferentially paired. The satellite i that cannot be paired with the satellite P1 and the remaining satellites j in the connected satellite set Cn except the satellite P1 are paired;

[0055] Q2: Repeat the operation of step Q1 for all satellites in the connected satellite set C n ;

[0056] Q3: According to the results of steps Q1 and Q2, judge whether the satellite i has a pairing satellite. If the satellite i has a pairing satellite, then remove the satellite i from set D and add the satellite i to the connected satellite set C n；

[0057] Q4: Repeat the operations of Q1 - Q3 for all indirectly synchronous satellites in set D, designate the subsequently found satellite P2 as the second-level phase synchronization reference satellite, and repeat the foregoing operations;

[0058] T11: If the number of satellites in the synchronizable satellite set C n+1 is 0 or there are no satellites in set D, then end the pairing process. Otherwise, let the positive integer n = n + 1 and repeat step T10.

[0059] Furthermore, each satellite in the distributed multi-satellite system has 8 phase synchronization horn antennas.

[0060] Beneficial effects: In view of the problems that there are a large number of distributed radar nodes and phase synchronization is required in collaborative work, on the one hand, in the prior art, the more complex the network structure and the longer the link, the more synchronization error accumulation will be; on the other hand, when the satellite moves, it will cause the position change of the nodes, or when a certain node is unstable, it may cause the entire network to collapse. The present invention provides a network optimization method for constructing a multi-node synchronization link of a spaceborne distributed radar. Compared with the prior art, the present invention can dynamically evaluate the signal-to-noise ratio and the mutual occlusion situation of multiple satellites, the system can adapt to environmental changes, optimize the connection between radar points, more effectively construct a radar network, and improve the performance of the network. BRIEF DESCRIPTION OF THE DRAWINGS

[0061] Figure 1 is the main flowchart of the network optimization method for constructing a multi-node synchronization link of a spaceborne distributed radar according to an embodiment of the present invention;

[0062] Figure 2 is a schematic diagram of determining a phase synchronization reference satellite and connection in the network optimization method for constructing a multi-node synchronization link of a spaceborne distributed radar according to an embodiment of the present invention;

[0063] Figure 3 is a schematic diagram of determining a first-level phase synchronization reference satellite and connection in the network optimization method for constructing a multi-node synchronization link of a spaceborne distributed radar according to an embodiment of the present invention;

[0064] Figure 4 is a schematic diagram of completion of the network optimization method for constructing a multi-node synchronization link of a spaceborne distributed radar according to an embodiment of the present invention;

[0065] Figure 5 is a simulation result diagram of the network optimization method for constructing a multi-node synchronization link of a spaceborne distributed radar according to an embodiment of the present invention;

[0066] Figure 6 is an optimal simulation result diagram of the network optimization method for constructing a multi-node synchronization link of a spaceborne distributed radar according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0067] As Figures 1 to 6 shown, the present invention provides a network optimization method for constructing a multi-node synchronization link of a spaceborne distributed radar.

[0068] Embodiment 1

[0069] For clarity and simplicity, we assume that each radar node transmits the same signal, usually denoted as where, is the envelope of the baseband signal, is the carrier frequency, is the initial phase, and t is time, and the unit of t is second.

[0070] For mathematical tractability, we assume that only one target is detected. It is considered that at the -th second after the transmitted pulse, the received backscattered signal can be modeled as , where A is the attenuation rate during the transmission process, is the time delay, is the noise.

[0071] The time delay is calculated according to the digital elevation model, and the calculation formula is .

[0072] Assuming that there is no phase error, array signal processing also uses the phase difference and time difference between the signals received by multiple radar nodes to estimate the direction of the signal, as well as to enhance the signal and suppress interference. Therefore, the layout of distributed coherent radar nodes can be regarded as an array, and each radar node is equivalent to an element in the array.

[0073] Delay processing is performed on the signals received by each node, and the expression is , , since kT is small, its impact on the amplitude can be ignored. Let , .

[0074] Since it is necessary to eliminate the phase offset caused by the different distances between multiple nodes and the target, it is necessary to process in , so , , since the connection of multiple nodes is not "one-to-one" pair-to-pair synchronization, the error will accumulate with transmission, and the error of the channel link cannot be eliminated according to the network connection. Therefore, this embodiment only considers the phase residual error caused by noise.

[0075] Assuming that each node has a phase residual error, the phase accumulation objective function of the phase noise residual error for the multi-node network connection is , where, to There are a total of n terms.

[0076] Assuming that the noise phases all conform to the Gaussian white noise zero-mean distribution, so the noise phase is the Gaussian white noise phase error generated by A points in the first-layer connection, satisfying the Gaussian distribution , the noise is the Gaussian white noise phase error generated by B points in the first-layer connection, satisfying the Gaussian distribution , and so on, the noise is the Gaussian white noise phase error generated by N points in the n-th layer connection, satisfying the Gaussian distribution 。

[0077] , When is monotonically decreasing, so 。

[0078] At this time, if it is required that the signal accumulation L is the largest, it is necessary to preferentially satisfy the maximum value in sequence, that is, to adopt a greedy strategy to make the first layer in the network connection be preferentially connected, and then adopt a greedy strategy to consider the second layer to be preferentially connected, and so on until all connectable nodes are connected.

[0079] The simulation verifies that the proposed link connection method is optimal according to the criterion of optimal phase accumulation in theoretical analysis. For the same 100 nodes, the connection methods of connecting 100 layers with one node in each layer and connecting 1 layer with 100 nodes in each layer are simulated. 1000 Monte Carlo experiments are respectively used for simulation and then the average value of L is calculated. At this time = 0.5, approximately simulating a phase error of 5°. As Figure 6 shown, the simulation results show that as the number of layers increases, the phase accumulation will gradually deviate from the theoretical value. And according to the greedy strategy, preferentially connecting the front layer numbers is more in line with the principle of optimal phase accumulation.

[0080] A network optimization method for constructing a multi-node synchronous link of a spaceborne distributed radar is as follows in specific implementation steps:

[0081] (1-0) Establishment of a distributed multi-satellite system. Construct a distributed multi-satellite system containing N satellites, and designate the Mth satellite as the master satellite, which is called "master satellite M" in the subsequent steps.

[0082] (2-0) Phase synchronization process.

[0083] (2-1) Transmission of state information. Each satellite sends its own position, attitude and other information to the master satellite in real time. The master satellite M needs to first store the number of phase synchronization horn antennas of each satellite.

[0084] (2-2) Determine the phase synchronization reference satellite based on the position and attitude information of each satellite obtained in step (2-1). Select the set E of satellites that need to perform phase synchronization, and determine the phase synchronization connection ability between satellites according to the mission requirements.

[0085] (2-3) Establishment of the phase synchronization reference satellite.

[0086] (2-4) Determine the satellite pairs that can directly perform phase synchronization.

[0087] (2-5) Determine the first-level reference satellite for phase synchronization and determine the satellite pairs that require indirect phase synchronization.

[0088] (2-6) Perform phase synchronization. The master satellite M sends the phase synchronization pairing results to each satellite, and each satellite transmits the phase synchronization signals according to the phase synchronization pairing results to achieve the phase synchronization of the entire system.

[0089] (3-0) Optimize the network stability.

[0090] (3-1) Define nodes and connections: Clearly define the nodes in the network and their connection methods.

[0091] (3-2) Evaluate the impact of node failure: Calculate the impact of a single node failure.

[0092] (3-2) Calculate the total expected value: Based on the current state of the network, calculate its total expected value.

[0093] (3-3) Optimize the network connections: Add connections to the original network to minimize the total expected value.

[0094] Embodiment 2

[0095] A network optimization method for constructing a multi-node synchronization link of an on-board distributed radar, as Figure 1 shown, includes the following steps:

[0096] (1-0) Establish a distributed multi-satellite system. Establish a distributed multi-satellite system composed of N satellites, and select the Mth satellite as the master satellite, hereinafter referred to as the master satellite M. In this embodiment, a distributed multi-satellite system including 10 satellites as shown in the figure is established, and each satellite has 8 phase synchronization horn antennas.

[0097] (2-0) Perform phase synchronization. As Figure 2 , Figure 3 , Figure 4 shown, the specific steps are as follows:

[0098] (2-1) Each satellite sends status information. Each satellite sends information such as its position and attitude at the start time, middle time, and end time of the current work task to the master satellite, and the master satellite M stores the number of phase synchronization horn antennas of each satellite in advance;

[0099] (2-2) Determine the reference satellite for phase synchronization based on the position and attitude information of each satellite obtained in (2-1). Put all the satellites that need phase synchronization into the set E, and determine the phase synchronization horns that can be connected to each other between two satellites according to the task.

[0100] (2-2-1) Combine with the determined synchronous horn antenna to judge the signal-to-noise ratio between satellites i in set E; for any two satellites, such as satellites A and B that need to perform phase synchronization, the signal-to-noise ratio discrimination method is as follows:

[0101] (2-2-1-1) Calculate the slant range R between satellites A and B AB , and the calculation method is as follows:

[0102] ,

[0103] In the formula, P A represents the position of satellite A, and P B represents the position of satellite B.

[0104] (2-2-1-2) Calculate the signal-to-noise ratio between satellites A and B, and the calculation method is as follows:

[0105] ,

[0106] In the formula, represents the transmit peak power of the phase synchronization horn antenna of satellite A, is the transmit gain of the phase synchronization horn antenna of satellite A, is the transmit gain of the phase synchronization horn antenna of satellite B, is the wavelength, is the processing gain, is the Boltzmann constant, is the temperature, is the bandwidth, is the receive noise figure, is the loss, and all the above parameters can be obtained through the distributed multi-satellite system. is the phase synchronization signal-to-noise ratio between satellites A and B.

[0107] (2-2-1-3) Perform signal-to-noise ratio judgment, and agree on the signal-to-noise ratio threshold SNR min .

[0108] If ≥ , it indicates that satellites A and B meet the signal-to-noise ratio threshold.

[0109] If < , it indicates that satellites A and B do not meet the signal-to-noise ratio threshold.

[0110] In this embodiment, the minimum signal-to-noise ratio Set it to 10 dB. Satellites 1, 4, and 10 meet the signal-to-noise ratio threshold. Satellites 2 and 9 meet the signal-to-noise ratio threshold. Satellites 3, 8, and 10 meet the signal-to-noise ratio threshold. Satellites 4 and 9 meet the signal-to-noise ratio threshold. Satellites 5, 6, and 7 meet the signal-to-noise ratio threshold. Satellites 6, 7, 8, and 9 meet the signal-to-noise ratio threshold. Satellites 8 and 10 meet the signal-to-noise ratio threshold.

[0111] (2-2-2) Judge the occlusion relationship between satellites i in set E. For any two satellites, such as satellites A and B that need to perform phase synchronization, the occlusion judgment method is as follows:

[0112] (2-2-2-1) For satellite k, perform the following calculations. Here, k is a positive integer less than N and not equal to A and B, representing different satellites, and N represents the total number of satellites.

[0113] ,

[0114] In the formula, represents the angle between the line connecting satellite B and satellite A and the line connecting satellite k and satellite A, represents the arccosine operation, represents the modulo operation. is the position of satellite A, is the position of satellite B, is the position of satellite k.

[0115] (2-2-2-2) Perform occlusion judgment.

[0116] If there exists a satellite k that meets the following conditions, it means that the phase synchronization link between satellites A and B is occluded. If there does not exist a satellite k that meets the following conditions, it means that the phase synchronization link between satellites A and B is not occluded.

[0117] or ,

[0118] Among them, represents the angle between the line connecting satellite B and satellite A and the line connecting satellite k and satellite A, represents the angle between the line connecting satellite A and satellite B and the line connecting satellite k and satellite B, represents the beam width of the synchronization horn antenna, which can be obtained through a distributed multi-satellite system.

[0119] In this embodiment, satellite 1 and satellite 3 are occluded by satellite 10, so there is occlusion; satellite 6 and satellite 10 are occluded by satellite 8, so there is occlusion; satellite 7 and satellite 8 are occluded by satellite 6, so there is occlusion; there is no occlusion between the remaining satellites in pairs.

[0120] Repeat steps (2-2-1) to (2-2-2) in (2-2-3). If there are pairwise satellites in set E that meet the SNR threshold and there is no occlusion, it is considered connectable. Put all connectable satellites into set D. If there are still satellites in set E, it means that there are satellites that cannot achieve phase synchronization. Then the master satellite M reports an error and feedbacks set E to the ground. For example, if a certain satellite is very far from other satellites and there is an impossible connection situation, this satellite cannot achieve phase synchronization anyway and cannot enter set D.

[0121] (2-2-4) Selection of phase synchronization reference satellite: If there is any satellite P and the most satellites i all meet the SNR threshold and there is no occlusion, that is, satellite P finds the most connectable satellites, then satellite P is the phase synchronization reference satellite.

[0122] If there are different satellites that can connect to the same maximum number of satellites i, that is, when finding the most connectable satellites, if there are multiple, randomly select one of them as the phase synchronization reference satellite P. In this embodiment, satellite 6 is the phase synchronization reference satellite, and the maximum number of satellites it can connect to is 4. Figure 2 、 3 、The phase reference satellite in 4 is represented as a blue circle.

[0123] (2-3) Judgment of satellite phase synchronization configuration, the steps are as follows:

[0124] (2-3-1) If there are satellite P and satellite i in (2-2-3) that meet the SNR threshold and there is no occlusion, then the phase synchronization configuration of the i-th satellite is a direct synchronization satellite.

[0125] If satellite P and satellite i do not meet the SNR threshold, or there is occlusion, then the phase synchronization configuration of the i-th satellite is an indirect synchronization satellite.

[0126] (2-3-2) Repeat (2-3-1) to determine the phase synchronization configuration of all satellites in set D.

[0127] Satellites belonging to direct synchronization are: satellite 5, satellite 7, satellite 8, satellite 9;

[0128] Satellites belonging to indirect synchronization are: satellite 1, satellite 2, satellite 3, satellite 4, satellite 10.

[0129] (2-4) The master satellite M determines the phase synchronization pairing satellites of the direct synchronization satellites.

[0130] (2-4-1) For the direct synchronization satellite i in set D, phase synchronization can be directly achieved through the paired transmission signal between satellite P and satellite i. Therefore, pair satellite i with satellite P. Remove satellite i from set D and add satellite i to the connected satellite set C1.

[0131] Perform operation (2-4-1) on all directly synchronized satellites in set D.

[0132] In this embodiment, after (2-4-1) and (2-4-2), the satellites included in the connected satellite set C1 are: satellite 5, satellite 7, satellite 8, satellite 9; as Figure 2 shown by the blue line segments, satellite 6 is paired with satellite 5, satellite 7, satellite 8, and satellite 9.

[0133] The remaining satellites in set D are: satellite 1, satellite 2, satellite 3, satellite 4, satellite 10.

[0134] (2-5) The master satellite M determines the phase synchronization pairing satellites for indirectly synchronized satellites, including the following steps.

[0135] (2-5-1) Initialize the positive integer n = 1.

[0136] (2-5-2) For the indirectly synchronized satellite i in set D, use the satellite j in the connected satellite set Cn for phase synchronization pairing. Cn is the set that can be connected after n judgments. For example, after initially determining the reference satellite, find the satellites that can be connected to it and put all these satellites into set C1. Then, find the indirectly synchronized reference satellite in C1 and find the satellites in the remaining set D that can be connected to the indirectly synchronized reference satellite, and put all these satellites into set C2, and so on. The specific steps are as follows:

[0137] (2-5-2-1) For the indirectly synchronized satellite i in set D, use the satellite j in the connected satellite set Cn to perform phase synchronization horn antenna selection, signal-to-noise ratio judgment, and occlusion judgment.

[0138] If the satellite P1 in the connected satellite set Cn and the most indirectly synchronized satellites i in set D all meet the signal-to-noise ratio threshold and there is no occlusion, then satellite P1 is designated as the first-level phase synchronization reference satellite, and the satellite P1 in the connected satellite set Cn is preferentially paired with satellite i. The satellite i that cannot be paired with satellite P1 and the remaining satellites j in the connected satellite set Cn after removing satellite P1 are paired.

[0139] (2-5-2-2) Repeat the operation of (2-5-2-1) for all satellites in the connected satellite set C n in.

[0140] (2-5-2-3) According to the results of (2-5-2-1) and (2-5-2-2), judge whether satellite i has a paired satellite. If satellite i has a paired satellite, then remove satellite i from set D and add satellite i to the connected satellite set C n。

[0141] (2-5-2-4) Repeat operations (2-5-2-1), (2-5-2-2), and (2-5-2-3) for all satellites in set D that are indirectly synchronized. Designate the subsequently found satellite P2 as the secondary phase synchronization reference satellite, and so on.

[0142] In this embodiment, the primary phase synchronization reference satellite is satellite 8. Figure 3 、 4 The primary phase synchronization reference satellite is represented as a green circle, and the satellites that are preferentially paired with it are satellites 3 and 10. They are connected by green line segments in Figure 3 、 4 Satellites that cannot be paired with it are satellites 1, 2, and 4. Among them, satellites 2 and 4 can be paired with satellite 9, and they are connected by green line segments in Figure 3 、 4 。

[0143] The secondary phase synchronization reference satellite is satellite 4. Figure 4 The secondary phase synchronization reference satellite is represented as a yellow circle in Figure 4 , and satellite 1 is paired with satellite 4, and they are connected by a yellow line segment in

[0144] (2-5-3) If the number of satellites in the set C of synchronizable satellites n+1 is 0 or there are no satellites in set D, end the pairing process; otherwise, let the positive integer n = n + 1, and repeat (2-5-2).

[0145] (2-6) Perform phase synchronization. The master satellite M sends the phase synchronization pairing result to each satellite, and each satellite transmits the phase synchronization signal according to the phase synchronization pairing result to achieve the phase synchronization of the entire system.

[0146] (3-0) Improve network stability. Put the line segments that meet the signal-to-noise ratio threshold and occlusion conditions but are not connected into set F. Assume that the probability of each node being damaged is independent, and the probability of affecting other nodes is independent.

[0147] (3-1) Define nodes and connections: Sort the nodes (i.e., each satellite) according to the number of nodes they are connected to from most to least, and label them respectively as , and the number of nodes connected to each node is denoted as (degree).

[0148] (3-2) Calculate the impact of a single node being damaged. When node is damaged, the nodes directly connected to it will be affected. For each node , the expected number of invalid nodes (including itself) caused by its damage is p × the number of affected nodes, where p is the probability of a single node being damaged.

[0149] (3-2) Calculate the total expected value. The sum of the impacts caused by the damage of any node in the network is the expected value of the entire network being damaged. The calculation formula is:

[0150] .

[0151] (3-3) Add the connections in set F to the original network to minimize the total expected value.

[0152] The present invention aims to provide a network optimization method for constructing a multi-node synchronization link of a spaceborne distributed radar. Compared with the prior art, the present invention can dynamically evaluate the signal-to-noise ratio and the mutual occlusion situation of multiple satellites, the system can adapt to environmental changes, optimize the connections between radar points, more effectively construct a radar network, and improve the performance of the network.

[0153] Finally, it should be noted that the above are only preferred embodiments of the present invention and are not used to limit the present invention. Although the present invention has been described in detail with reference to the embodiments, for those skilled in the art, they can still modify the technical solutions recorded in the foregoing embodiments, or perform equivalent replacements on some of the technical features. However, any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A network optimization method for establishing multi-node synchronous links of a spaceborne distributed radar, characterized in that: The following steps are involved: Step 1: Establish a distributed multi-satellite system: Establish a distributed multi-satellite system consisting of N satellites, select the Mth satellite as the master satellite, and each satellite has T phase-synchronized horn antennas; Step 2: Perform phase synchronization, including the following steps: S1: Each satellite in the distributed multi-satellite system sends a status message: Each satellite sends information including the position and attitude of the current task start time, intermediate time and end time to the master satellite M. The master satellite M stores the number of phase-synchronized horn antennas of each satellite in advance; S2: Determine the phase synchronization reference satellite based on the position and attitude information of each satellite obtained in step S1, put all satellites that need phase synchronization into set E, and determine the phase synchronization horn antennas that can connect any two satellites based on the mission; S3: Perform satellite phase synchronization configuration judgment to identify whether the satellite phase synchronization configuration in the distributed multi-satellite system is a direct synchronous satellite or an indirect synchronous satellite; S4: The main satellite M determines the phase synchronization pairing satellite of the direct synchronous satellite; S5: The main satellite M determines the phase synchronization pairing satellite of the indirect synchronous satellite; S6: Perform phase synchronization: The master satellite M sends the phase synchronization pairing result to each satellite. Each satellite transmits the phase synchronization signal according to the phase synchronization pairing result to achieve phase synchronization of the distributed multi-satellite system. Step 3: Improve network stability, including the following steps: S7: When the probability of each node being damaged is independent and the probability of affecting other nodes is independent, put the unconnected line segments that meet the signal-to-noise ratio threshold and occlusion conditions into the set F; S8: Define nodes and connections: Sort nodes by the number of nodes they are connected to, and mark them as , each node The number of connected nodes is recorded as ; S9: Calculate the impact of single node damage: When the node When damaged, the directly connected nodes will be affected, for each node , the expectation of the number of invalid nodes caused by its damage is p × the number of affected nodes, where p is the probability of a single node being damaged; S10: Calculate the total expected value: The cumulative impact of damage to any node in the network is the expected value of the damage to the entire network. The calculation formula is: ; S11: Add connections in set F to the original network to minimize the total expected value.

2. The network optimization method for establishing multi-node synchronous links of a spaceborne distributed radar according to claim 1, characterized in that: In step S2, the phase synchronization reference satellite is determined based on the acquired position and attitude information of each satellite, including the following steps: T1: Determine the signal-to-noise ratio between satellites i in the set E by combining the determined phase-synchronized horn antenna; T2: Determine the occlusion relationship between satellites i in the set E; T3: Repeat steps T1 and T2. If there are two satellites i in set E that meet the signal-to-noise ratio threshold and there is no occlusion, they are considered connectable and all connectable satellites are placed in set D. If there are still satellites in the set E, it means that there are satellites that cannot be phase synchronized, then the master satellite M reports an error and feeds the set E back to the ground; T4: Select the phase synchronization reference satellite: If there is any satellite P and the maximum number of satellites i that meet the signal-to-noise ratio threshold and there is no occlusion, that is, satellite P finds the most connectable satellites, then satellite P is the phase-synchronized reference satellite; If there are different satellites that can connect to the same number of satellites i at most, that is, when looking for the most connectable satellites, if there are multiple satellites, one of them is randomly selected as the phase synchronization reference satellite P.

3. The network optimization method for establishing multi-node synchronous links of a spaceborne distributed radar according to claim 2, characterized in that: In step T1, for any two satellites A and B in the set E, phase synchronization is required. The signal-to-noise ratio determination method includes the following steps: K1: Calculate the slant distance between satellites A and B , the calculation expression is ,in, represents the position of satellite A, represents the position of satellite B; K2: Calculate the signal-to-noise ratio between satellites A and B. The calculation expression is: ,in, represents the peak power transmitted by the phase-synchronized horn antenna of satellite A, is the transmission gain of the phase-synchronized horn antenna of satellite A, is the transmission gain of the phase-synchronized horn antenna of satellite B, is the wavelength, is the processing gain, is the Boltzmann constant, is the temperature, is the bandwidth, is the receive noise figure, It is loss, is the phase synchronization signal-to-noise ratio between satellite A and satellite B; K3: Determine the signal-to-noise ratio and agree on the signal-to-noise ratio threshold based on actual conditions ; like ≥ , it indicates that satellite A and satellite B meet the signal-to-noise ratio threshold; like < , it indicates that satellite A and satellite B do not meet the signal-to-noise ratio threshold.

4. The network optimization method for establishing multi-node synchronous links of a spaceborne distributed radar according to claim 2, characterized in that: In step T2, for any two satellites A and B in the set E, phase synchronization is required. The method for determining occlusion includes the following steps: K4: Calculate the number of satellites K, where k is a positive integer less than N and not equal to A and B, representing different satellites. N represents the total number of satellites. The calculation expression is: ,in, It is expressed as the angle between the line connecting satellite B and satellite A and the line connecting satellite k and satellite A, Indicates the inverse cosine operation, Represents the modulo operation, is the position of satellite A, is the position of satellite B, is the position of satellite k; K5: Perform occlusion judgment: If satellite K satisfies or , it means that there is an obstruction in the phase synchronization link between satellite A and satellite B; If satellite K does not satisfy or , it means that there is no obstruction in the phase synchronization link between satellite A and satellite B; in, It is expressed as the angle between the line connecting satellite B and satellite A and the line connecting satellite k and satellite A, It is expressed as the angle between the line connecting satellite A and satellite B and the line connecting satellite k and satellite B, It represents the beam width of the synchronized horn antenna, which can be obtained through a distributed multi-satellite system.

5. The network optimization method for establishing multi-node synchronous links of a spaceborne distributed radar according to claim 2, characterized in that: Step S3 determines the satellite phase synchronization configuration, including the following steps: T5: If satellite P and satellite i meet the signal-to-noise ratio threshold and there is no obstruction, the phase synchronization configuration of the i-th satellite is a direct synchronous satellite; If satellite P and satellite i do not meet the signal-to-noise ratio threshold, or there is occlusion, the phase synchronization configuration of the i-th satellite is an indirect synchronous satellite; T6: Repeat step T5 to determine the phase synchronization configuration of all satellites in set D.

6. The network optimization method for establishing multi-node synchronous links of a spaceborne distributed radar according to claim 5, characterized in that: In step S4, the master satellite M determines the phase synchronization paired satellite of the direct synchronous satellite, which includes the following steps: T7: For the direct synchronous satellite i in set D, phase synchronization can be achieved directly through the mutual transmission signal between satellite P and satellite i. Therefore, satellite i is paired with satellite P, satellite i is removed from set D, and satellite i is added to the connected satellite set C1; T8: Perform the operation of step T7 on all direct synchronous satellites in set D.

7. The network optimization method for establishing multi-node synchronous links of a spaceborne distributed radar according to claim 1, characterized in that: In step S5, the master satellite M determines the phase synchronization paired satellite of the indirect synchronous satellite, including the following steps: T9: Initialize the positive integer n=1; T10: For the indirectly synchronized satellite i in the set D, phase synchronization pairing is performed using satellite j in the connected satellite set Cn. Cn is the set confirmed to be connectable after n times of judgment. The specific steps are as follows: Q1: For the indirectly synchronized satellite i in the set D, use the satellite j in the connected satellite set Cn to perform phase synchronization horn antenna selection, signal-to-noise ratio judgment, and obstruction judgment; If satellite P1 in the connected satellite set Cn and the most indirectly synchronized satellite i in the set D both meet the signal-to-noise ratio threshold and there is no obstruction, then satellite P1 is determined as the first-level phase synchronization reference satellite, and satellite P1 in the connected satellite set Cn is paired with satellite i first. Satellite i that cannot be paired with satellite P1 is paired with the remaining satellite j in the connected satellite set Cn excluding satellite P1. Q2: For the connected satellite set C n Repeat step Q1 for all satellites in the Q3: Based on the results of steps Q1 and Q2, determine whether satellite i has a paired satellite. If satellite i has a paired satellite, then remove satellite i from set D and add satellite i to the connected satellite set C. n； Q4: Repeat Q1-Q3 for all indirectly synchronized satellites in set D, set the subsequently found satellite P2 as the secondary phase synchronization reference satellite, and repeat the above operations; T11: If the synchronous satellite set C n+1 If the number of satellites in is 0 or there are no satellites in set D, the pairing process ends. Otherwise, let the positive integer n = n + 1 and repeat step T10.

8. The network optimization method for establishing multi-node synchronous links of a spaceborne distributed radar according to claim 1, characterized in that: Each satellite in the distributed multi-satellite system has eight phase-synchronized horn antennas.

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