CN113315568A - Satellite navigation system and method for topologically planning inter-satellite link network - Google Patents
Satellite navigation system and method for topologically planning inter-satellite link network Download PDFInfo
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Abstract
The invention provides a satellite navigation system and a method for topologically planning an inter-satellite link network thereof.A general design idea is to sequentially solve the inter-satellite link topology in each time slot, update algorithm parameters to further solve the inter-satellite link topology of the next time slot after completing the inter-satellite link network topology solution of all the time slots, perform global optimization, and finally output a topology plan of a link establishment period.
Description
Technical Field
The invention relates to the field of satellites, in particular to a satellite navigation system and a method for topologically planning an inter-satellite link network thereof.
Background
The inter-satellite link is a wireless link established between satellites, and in the navigation system, the inter-satellite link is established to realize the communication and ranging functions between the satellites, so that the navigation ephemeris can be updated more frequently by utilizing the inter-satellite link communication, the service performance of the navigation system is improved, the forwarding of measurement and control information is realized, and the navigation constellation is indirectly measured and controlled; the distance measurement between satellites is carried out by utilizing the inter-satellite link, the orbit determination precision of the satellites can be improved, or the autonomous operation of a navigation constellation is realized under the condition of no ground station support. At present, research or application of inter-satellite link technology is carried out on all large global navigation systems. The inter-satellite link of the time division system is an advanced inter-satellite link system, each satellite is provided with a pair of directional controllable antennas under the system, the directions of the antennas are switched at different moments, and the inter-satellite link establishment among different satellites is realized, so that the topological structure of an inter-satellite link network is time-varying. The inter-satellite link of the system has the outstanding characteristics of low cost, high efficiency, flexible network topology, excellent performance and the like.
The inter-satellite link network topology of the system is planned in advance, namely, inter-satellite links are established between each satellite and an appointed target satellite at different moments according to pre-calculated satellite orbit parameters and a certain method and strategy. The duration of one link establishment of two satellites is called a time slot, a link establishment period is formed by a plurality of time slots, the topology planning of the inter-satellite link network can be completed by appointing the satellite link establishment relation of each time slot in the constellation regression period, and the time-varying rule of the inter-satellite link network topology is determined.
And finishing data transmission and inter-satellite ranging by the inter-satellite link network based on the inter-satellite link network topology planning result. The inter-satellite link network topology planning result is closely related to the performance of the inter-satellite link network, and directly influences important indexes of measurement and observation data of a satellite, the satellite orbit determination precision, the network information transmission delay, the network communication throughput and the like. Therefore, for the time-varying navigation system inter-satellite link network, the communication, measurement and expansion use requirements of the inter-satellite link are comprehensively considered, and the design of the optimized network topology planning method has very important significance.
At present, although there are few researches on network topology planning methods of time-varying inter-satellite links of a navigation system, most of the researches are not deep enough, and the main technical defects include:
(1) the inter-satellite link mainly has the functions of communication and measurement, but the partial methods are difficult to realize the communication and the measurement at the same time, one function is taken as an optimization target of the inter-satellite link network topology planning, the requirement of the other function is ignored, the performance of the inter-satellite link network is unbalanced, and the method is difficult to be applied in practice.
(2) The existing method only considers the use requirements of the inter-satellite link in the system, and cannot consider the use requirements of the inter-satellite link for other extended users outside the system. And the residual inter-satellite link resources are distributed to users outside the system under the condition that the minimum inter-satellite link resources meet all use requirements and performance constraints of the navigation system, so that the use efficiency of the inter-satellite links can be improved.
(3) In part of the existing methods, the consideration of the communication performance is based on the point-to-point communication requirement of the whole network, and the communication performance of the inter-satellite link network can be further improved by taking the communication requirement of the ground station and the overseas satellite as an optimization target according to the communication characteristics of the navigation system.
(4) Part of the existing methods take an optimal satellite geometric configuration (DOP value) as an optimization target, the improvement effect of the DOP value on the satellite orbit determination precision becomes limited along with the reduction of the DOP value, and inter-satellite link resources are wasted to a certain extent if the optimization of the geometric configuration is pursued. Therefore, under the condition of meeting the constraint basis of a certain quantity of inter-satellite links and DOP values, optimization of geometric configuration is not sought, and the overall performance of the network can be further improved by allocating inter-satellite link resources to communication requirements or expanding user requirements.
(5) In part of the existing methods, the inter-satellite observation quantity and the satellite geometric configuration are used as indexes for measuring performance, but for a navigation system, the constellation autonomous navigation performance is closely related to satellite selection, different satellite selections have certain influence on satellite orbit determination precision under the condition of the same inter-satellite link quantity or the same DOP value, and consideration should be added during inter-satellite link network topology planning.
Disclosure of Invention
In view of the above technical problem, the present invention provides a satellite navigation system, including:
a satellite configured to perform the following actions:
determining a chain-building relation among satellites in each chain-building period and a visual relation between the satellites and a ground station according to a time range of inter-satellite link network topology planning; classifying the satellite nodes, and defining the satellite nodes as node satellites when the satellite is in the observation range of the ground station; when the satellite is not in the observation range of the ground station, defining the satellite as a non-node satellite;
dividing the time slots in a link establishing period into P complete combinations and Q residual time slots, wherein each complete combination comprises N time slots, N is more than Q and is not less than 0, N is (m 2/m1] +1, and [ ] represents rounding up, and is the number of node satellites and the number of non-node satellites;
step three, defining the 1 st to N-1 th time slots in each complete combination as data transmission time slots, and defining the Nth time slot as a measurement time slot; the definition of the Q remaining time slots is consistent with the 1 st to the Q th time slot definition in each complete combination; sequentially solving the network topology in each data transmission time slot in a link establishment period, and further solving the network topology in the measurement time slot;
step four, after the network topology solution of all the data transmission time slots and the measurement time slots in a link establishment period is completed, remaining satellite idle time slots are provided for expansion users outside the system, and inter-satellite link allocation with the expansion users outside the system is completed;
step five, after the inter-satellite link allocation of the user is completed and expanded outside the system, if the satellite is still in an idle state, the network topology of the idle time slot is globally optimized; and
a ground station configured to communicate with a non-nodal satellite over an inter-satellite link.
The invention also provides a method for topologically planning an inter-satellite link network of the satellite navigation system, which comprises the following steps:
determining a chain-building relation among satellites in each chain-building period and a visual relation between the satellites and a ground station according to a time range of inter-satellite link network topology planning; classifying the satellite nodes, and defining the satellite nodes as node satellites when the satellite is in the observation range of the ground station; when the satellite is not in the observation range of the ground station, defining the satellite as a non-node satellite;
dividing the time slots in a link establishing period into P complete combinations and Q residual time slots, wherein each complete combination comprises N time slots, N is more than Q and is not less than 0, N is (m 2/m1] +1, and [ ] represents rounding up, and is the number of node satellites and the number of non-node satellites;
step three, defining the 1 st to N-1 th time slots in each complete combination as data transmission time slots, and defining the Nth time slot as a measurement time slot; the definition of the Q remaining time slots is consistent with the 1 st to the Q th time slot definition in each complete combination; sequentially solving the network topology in each data transmission time slot in a link establishment period, and further solving the network topology in the measurement time slot;
step four, after the network topology solution of all the data transmission time slots and the measurement time slots in a link establishment period is completed, remaining satellite idle time slots are provided for expansion users outside the system, and inter-satellite link allocation with the expansion users outside the system is completed;
and step five, after the inter-satellite link allocation of the user is completed and expanded outside the system, if the satellite is still in an idle state, performing global optimization on the network topology of the idle time slot.
And further, according to the first step to the fifth step, sequentially finishing the inter-satellite link network topology planning of all link establishment periods in the planning time range.
Further, in the third step, the network topology solving in the data transmission time slot includes:
defining a complete bipartite graph, wherein the neutralization is a point set, the edge set represents a node satellite set, the non-node satellite set and all inter-satellite links with link establishment conditions between the node satellite set and the non-node satellite set; and solving the maximum matching problem of the bipartite graph so as to complete the distribution of the inter-satellite links between the non-node satellite and the node satellite.
Further, in the third step, the network topology solution in the measurement time slot includes the following steps:
step 31, judging whether the idle state satellite of the current time slot reaches an observation PDOP value threshold;
step 32, extracting all satellite nodes which are in an idle state and do not reach a PDOP value threshold in the current ranging time slot to form a node set, and meanwhile, sequencing the nodes in the set from large to small according to the current observed PDOP value;
step 33, extracting a first satellite node in the set, forming a set by the satellite nodes which can build a link with the satellite node, and sequencing all the satellite nodes in the set in sequence according to the priority;
and step 34, selecting the 1 st satellite node in the set, and planning an inter-satellite link between the satellite node and the satellite node, wherein the satellite node and the satellite node are not in an idle state any more.
Further, the inter-satellite link planning of all nodes in the current time slot is completed in sequence according to the steps 31 to 34, and the rest satellite nodes without chain building members are placed in an idle state.
Further, in the step 33, the priority definitions are classified into 3 categories, and sequentially include, according to the order of decreasing importance degree:
the class 1 priority is based on the number of established links of the target satellite and the source satellite, is sorted from small to large according to the number of established links of the target satellite and the source satellite, and has the highest priority of the satellite node with the least number of established links of the source satellite;
the type 2 priority is based on the orbit type of the target satellite, the target satellites are classified according to the orbit type, the same-orbit target satellite located in the same orbit plane with the source satellite has low priority, and the different-orbit target satellite located in different orbit planes has high priority;
and the 3 rd type priority is based on the improvement degree of the target satellite on the PDOP value observed by the source satellite, the improvement values are sorted from large to small, and the target satellite with the maximum improvement value has the highest priority.
Further, when the priority orders of the same class are the same, the next priority is compared.
Further, in the fifth step, the global optimization includes the following steps:
step 52, extracting the satellite nodes in the idle state in the current time slot, and solving according to a network topology solving method in a measurement time slot, wherein the observation PDOP value is not set at the moment;
step 53, dividing the rest satellite nodes in the idle state in the time slot into a node satellite set and a non-node satellite set, and if yes, switching to the next time slot for solving; otherwise, solving according to a network topology solving method in a data transmission time slot.
The beneficial effects of the invention include:
(1) the multiple time slots in a link establishment period are divided into multiple combinations according to rules, and a special topology planning method is designed for the different types of time slots in the combinations, so that the communication and measurement requirements of the inter-satellite link network of the navigation system are considered, the network has excellent performance in the aspects of measurement and communication requirements, and the overall performance is balanced;
(2) besides basic functional requirements of an inter-satellite link network of the navigation system, the use requirements of expansion users outside the system are considered, and inter-satellite link resources are reserved or provided for specified expansion users on the premise of not influencing the use requirements of the inter-satellite link of the navigation system, so that the comprehensive service performance and the network utilization rate of the navigation system are improved;
(3) aiming at the communication characteristics and requirements of a ground station and a non-node satellite in a navigation system, a network topology planning algorithm is designed, the operation efficiency is high, the algorithm model is concise in description, the calculation result realizes one-hop transmission of information between the non-node satellite and the ground station, and the communication performances such as time delay, throughput, transmission efficiency and the like of an inter-satellite link network are greatly improved;
(4) aiming at the measurement characteristics and requirements of satellite orbit determination in a navigation system, a satellite selection principle of satellite orbit determination is introduced, satellite priority is set, the inter-satellite link observation quality is ensured and optimized, meanwhile, observation quantity threshold constraint is provided, and the time slot utilization rate and the network comprehensive efficiency are improved.
The conception, the specific structure and the technical effects of the present invention will be further described with reference to the accompanying drawings to fully understand the objects, the features and the effects of the present invention.
Drawings
Fig. 1 to 5 are schematic diagrams of matrices in an embodiment of the present invention.
Detailed Description
In the description of the embodiments of the present invention, it should be understood that the terms "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", "clockwise", "counterclockwise", etc., indicate orientations or positional relationships based on those shown in the drawings, and are only for convenience of description and simplicity of description, but do not indicate or imply that the referred devices or elements must have a specific orientation, be constructed and operated in a specific orientation, and thus, should not be construed as limiting the invention. The drawings are schematic diagrams or conceptual diagrams, and the relationship between the thickness and the width of each part, the proportional relationship between the parts and the like are not completely consistent with actual values.
The general idea of the inter-satellite link network topology planning method is to sequentially solve the inter-satellite link topology in each time slot, update algorithm parameters to further solve the inter-satellite link topology of the next time slot after the inter-satellite link topology solution of one time slot is completed, perform global optimization after the inter-satellite link network topology solution of all the time slots in a link establishment period is completed, and finally output the topology planning of one link establishment period.
The adopted technical scheme specifically comprises the following steps:
A) network topology based on inter-satellite linksDetermining the constructable link relation V, V between satellites in each link construction period ij1 represents that a link can be established between satellite i and satellite j, v ij0 represents the link between the satellite i and the satellite j and the visual relationship between the satellite and the ground station; classifying the satellite nodes, and defining the satellite as a node satellite when the satellite is in the observation range of the ground station; a satellite is defined as a non-nodal satellite when the satellite is not within the field of view of the ground station.
B) According to the number of the node satellites and the number of the non-node satellites, N time slots are divided into a group, M time slots are selected as a link establishment period, P complete combinations are contained in the period, and Q residual time slots are contained, namely M is equal to P multiplied by N + Q. Suppose there is m at a time1A single node satellite and m2A non-nodal satellite, then N ═ m2/m1]+1，[]Representing a rounding up.
C) Defining 1 to N-1 time slots in a group of N time slots as data transmission time slots, wherein the Nth time slot is a measurement time slot; the definition of the Q remaining slots is consistent with the definition of 1 to Q slots in each set of N slots. And sequentially solving the network topology in each data transmission time slot in a link establishment period, and further solving the network topology structure in the measurement time slot.
The specific method for solving the topology of the data transmission time slot network comprises the following steps:
the communication requirement of the inter-satellite link of the navigation system is mainly the communication between the ground station and the non-node satellite, and the data transmission time slot network topology planning aims at improving the data transmission efficiency between the ground station and the non-node satellite.
In order to improve the data transmission performance and efficiency of the network, a link is established between a node satellite and a non-node satellite, so that the communication between a ground station and the node satellite and the non-node satellite is realized; meanwhile, the link establishment frequency of the node satellite and the non-node satellite is increased, so that one-hop transmission of data information between the non-node and the ground station can be realized under the condition of no packet loss of data, the network routing complexity is reduced, and the transmission bandwidth is saved.
Therefore, the network topology planning in the data transmission time slot needs to complete the inter-satellite link allocation between the node satellite and the non-node satellite, and meanwhile, the link establishment frequency between each non-node satellite and the node satellite in one link establishment period needs to be ensured. In the method, the link establishment frequency of the node satellite and the non-node satellite is ensured through the time slot grouping in the step B, when the solution is carried out in each communication time slot, the maximum number of inter-satellite links between the non-node satellite and the node satellite are distributed only by ensuring that the inter-satellite link establishment constraint is met, and the problem can be converted into the maximum matching problem of the bipartite graph.
And defining a complete bipartite graph G (X, Y and E), wherein X and Y are point sets, E is an edge set, X represents a node satellite set, Y represents a non-node satellite set, and E represents all inter-satellite links with link establishment conditions between the node satellite set X and the non-node satellite set Y. And (3) the maximum matching problem of the bipartite graph G (X, Y, E) is solved, so that the distribution of the inter-satellite links between the non-node satellite and the node satellite can be completed.
In general, the maximum matching result is not unique, and considering the requirements of satellite orbit determination and time synchronization, each satellite and different target satellites can build a link to increase the inter-satellite link observation quantity and improve the orbit determination result. Therefore, different maximum matching results are selected for different data transmission time slots.
In a link establishment period, when the number of non-node satellites is m2Less than or equal to the number m of node satellites1In time, the maximum matching result can ensure that one data transmission time slot can be used for distributing one node satellite for each non-node satellite to establish an inter-satellite link; when the number of non-node satellites is m2Greater than the number m of the node satellites1Then, the maximum matching result can only be m at most1One non-node satellite is distributed to one node satellite to establish an inter-satellite link, and m which is not distributed remains2-m1And (4) allocating the non-node satellite in the next data transmission time slot, and repeating the steps until all the non-node satellites are allocated. And finally, ensuring 1 to N-1 transmission time slots in 1 time slot combination, and at least allocating one inter-satellite link between each non-node satellite and the node satellite.
The specific method for solving the topology of the measurement time slot network comprises the following steps:
and (3) measuring the inter-satellite link network topology plan in the time slot, mainly aiming at ensuring and improving the measurement performance of the inter-satellite link network. The method comprehensively considers three factors of inter-satellite link observation quantity, observation data geometric configuration and observation satellite type, and completes inter-satellite link network topology planning in the ranging time slot. The inter-satellite link observation quantity specifically refers to the quantity of inter-satellite links establishing links with different target satellites; the observation data geometric configuration specifically refers to the geometric distribution of all the link-building satellites and is described by a PDOP value; the observation satellite type specifically refers to a target satellite type of a link, and is divided into a co-orbit observation satellite and an off-orbit observation satellite.
Selecting different target satellites for any satellite node to establish an inter-satellite link can generate different influences on measurement performance, therefore, when the measurement time slot network topology is solved, a target satellite node with the highest priority is preferably selected for each satellite node to establish a link, and the definition of the priority of the method is specifically as follows:
the definition of the priority is divided into 3 classes, the importance degree is decreased in sequence, namely, the priority of the 1 st class is greater than the priority of the 2 nd class is greater than the priority of the 3 rd class, and the priority of the same class is compared with the next priority when the priority of the same class is the same.
The measurement time slot network topology is solved based on the priority result of the node, and considering that the improvement effect of the measurement time slot network topology on the satellite orbit determination precision becomes more and more limited along with the increase of the inter-satellite link observation quantity and the reduction of the observation PDOP value, an observation PDOP value threshold is set, when the observation PDOP value reaches the threshold, the inter-satellite link planning is not carried out on the satellite, and the inter-satellite link resource of the satellite is provided with other services. The solving steps of the measurement time slot network topology are as follows:
(1) judging whether the idle state satellite of the current time slot reaches an observation PDOP value threshold or not;
(2) extracting all satellite nodes which are in an idle state and do not reach a PDOP value threshold in the current ranging time slot to form a node set A, and meanwhile, sequencing the nodes in the set A from large to small according to the current observed PDOP value;
(3) extracting the first satellite node a in A1Will communicate with satellite a1The satellite nodes which can build the chain form a set B, and all the satellite nodes in the set B are sequentially ordered according to the three types of priorities;
(4) selecting the 1 st satellite node B in B1At satellite node a1And satellite node b1Inter-satellite links are planned, in which case the satellite node a1And satellite node b1No longer in an idle state;
(5) and (4) sequentially finishing inter-satellite link planning of all nodes in the current time slot according to the steps, and placing the rest satellite nodes without chain building members in an idle state.
D) After the network topology solution of all data transmission time slots and measurement time slots in a link establishment period is completed, remaining satellite idle time slots still exist, the idle time slots are used by expansion users outside the system according to actual requirements at different moments, and inter-satellite link allocation with the expansion users outside the system is completed according to actual conditions.
E) After the inter-satellite link distribution of the user is expanded outside the system, if the satellite is still in an idle state, the network topology of the idle time slot is globally optimized, and the inter-satellite link network topology planning of a link establishment period is completed.
The global optimization of the inter-satellite link network topology for a link establishment period is to perform the reallocation of inter-satellite links for satellites in idle working states in the period, so as to further improve the communication performance and the measurement performance of the inter-satellite link network. The global optimization solution process is as follows:
(1) sequentially selecting all time slots in a link establishment period, and executing the following steps (2) and (3);
(2) extracting satellite nodes in an idle state in a current time slot, and solving according to a network topology solving method in a measurement time slot, wherein an observation PDOP value is not set at the moment;
(3) dividing the rest satellite nodes in idle state in the time slot into a node satellite set X and a non-node satellite set Y, if so, dividing the rest satellite nodes in idle state in the time slot into a node satellite set X and a non-node satellite set Y
Or
Switching to the next time slot for solving; otherwise, solving according to a network topology solving method in a data transmission time slot.
F) And D, sequentially finishing the inter-satellite link network topology planning of all link establishment periods in the planning time range according to the steps A to E.
The planning method is further explained by selecting a typical satellite constellation containing 30 satellites and defining a link establishment period containing 20 time slots, wherein the satellites in the constellation are respectively represented by numbers 1-30, the satellites 1-8 are positioned on the same orbital plane, the satellites 9-16 are positioned on the same orbital plane, the satellites 17-24 are positioned on the same orbital plane, and the satellites 25-30 are positioned on the same orbital plane, and simultaneously selecting a link establishment period to plan the inter-satellite link network topology of the constellation. And describing a network topology planning result by using a planning table matrix L, wherein rows of the L represent time slots, columns of the L represent satellites, an element L (i, j) ═ k represents that an inter-satellite link is established between a satellite node j and the satellite node k in the ith time slot, and if L (i, j) ═ 0 represents that the satellite node j is in an idle state in the ith time slot. Row vector L of inter-satellite link network topology available planning table matrix L in one time slotiAnd representing the network topology plan of the intersatellite link in the ith time slot.
Step A) firstly, analyzing the chain-building relationship and satellite-ground visibility between the satellites at the time corresponding to the chain-building period, wherein the chain-building relationship between the satellites mainly considers whether the satellites are geometrically visible or not and whether the satellites are within the beam coverage range of the opposite antenna or not, and the chain-building relationship between the satellites at the time is shown in figure 1. Meanwhile, a Beijing station and a third-generation station are selected as ground stations, the satellites are divided into node satellites and non-node satellites, and the satellite classification result is shown in the following table and totally comprises 15 node satellites and 15 non-node satellites.
| |
1/2/3/4/9/16/18/19/20/25/26/27/28/29/30 |
| |
5/6/7/8/10/11/12/13/14/15/17/21/22/23/24 |
Step C) defining 2 time slots in a combination, wherein the 1 st time slot is a data transmission time slot, the 2 nd time slot is a measurement time slot, namely 20 time slots in a link establishment period, an odd time slot is a data transmission time slot, an even time slot is a measurement time slot, and the time slot combination result is shown in the figure. And solving the network topology in each data transmission time slot and measurement time slot in a link establishment period in turn.
Firstly, solving the topology of the inter-satellite link network in the data transmission time slot, describing the network structure in the time slot by adopting a complete bipartite graph G (X, Y, E), forming a node set X by 15 node satellites in the current time slot combination, forming a node set Y by 15 non-node satellites, determining an edge set E of the bipartite graph according to the inter-satellite link-building relation calculated in the step A, calculating the maximum matching result of the bipartite graph, distributing a node satellite for each non-node satellite according to the maximum matching result, and building an inter-satellite link between two satellite nodes. The calculation result of the current data transmission time slot is
l1＝[7 8 5 21 3 30 1 2 15 16 25 18 19 20 9 10 26 12 13 14 4 28 29 27 11 17 24 22 23 6]
Because only 1 data transmission time slot is contained in one time slot combination of the link establishment period, the data transmission time slot enters the next time slot combination after being calculated, the inter-satellite link network topology of the data transmission time slot in the next combination is solved, the solving process is basically consistent with the process, a complete bipartite graph G (X, Y, E) is adopted to describe the network structure in the current time slot, and the solving are carried out1The maximum matching result of different time slots. The calculation result of the current data transmission time slot is
l3＝[15 21 11 24 25 29 16 27 12 18 3 9 26 28 1 7 19 10 17 22 2 20 30 4 5 13 8 14 6 23]
From l3The topological result of the intersatellite link network of the time slot can be seen, and l is selected1Maximum matching result of different time slots,/1Time slot and3the network topology planning results of the time slots are different, and the non-node satellite and the different node satellites establish inter-satellite links. The inter-satellite link network topology solution of all data transmission time slots in a link establishment period is completed in sequence according to the steps, and the result of the solution of all data transmission time slots is shown in fig. 2.
After the inter-satellite link network topology in the data transmission time slot is solved, the inter-satellite link network topology of each ranging time slot in a link establishment period is solved, a solving model is designed according to the method, and an observation threshold PDOP is set to be 1.55 according to the constellation scale and the characteristics of the embodiment. First, the first ranging slot is solved, i.e. solution l2。l2Time slot non-existence has been reachedThe satellites of the PDOP value observation threshold form a set A according to the previous PDOP value observation, and are sorted from big to small; extracting the first satellite node a1Will communicate with satellite a1The satellite nodes which can build the chain form a set B, and all the satellite nodes in the set B are sequentially ordered according to the three types of priorities; selecting the 1 st satellite node B in B1At satellite node a1And satellite node b1Inter-satellite links are planned; and analogizing in sequence to complete the inter-satellite link planning of all nodes, and placing the rest satellite nodes without chain building members in an idle state, wherein l is the time2The planning result of the inter-satellite link of the time slot is as follows:
l2＝[9 16 20 25 12 17 11 24 1 21 7 5 15 0 13 2 6 23 22 3 10 19 18 8 4 0 0 0 0 0]
finish solving2After the inter-satellite link of the time slot is planned, the next distance measurement time slot l is continuously solved4Inter-satellite link planning of time slots, in this embodiment, to the 5 th ranging slot l10Then, all the nodes have reached the observation threshold PDOP of 1.55, the inter-satellite link network topology solution of the ranging time slot is completed, and the inter-satellite link network topology planning result at this time is shown in fig. 3.
Step D) as can be seen from the result of fig. 3, 41% of idle time slots still remain in the link establishment period, but the planning result of the inter-satellite link network topology can already meet various use requirements in the navigation system, and these idle time slots can be provided for extended users outside the system according to actual needs. Assuming that there is a low earth orbit satellite user who needs to use inter-satellite link service, a certain number of inter-satellite links are allocated to provide service for the low earth orbit satellite by calculating the chain-establishing relationship between the low earth orbit satellite and the satellite in the navigation system, and the result of the inter-satellite link network topology planning is shown in fig. 4, and numbers 50 and 51 are used to represent 2 low earth orbit satellites.
And E) after the inter-satellite link allocation of the user with the system external expansion is completed, sequentially searching 20 time slots in a link establishment period, judging whether the satellite is still in an idle state, extracting the satellite nodes in the idle state in the current time slot, sequentially solving according to a network topology solving method in a measurement time slot and a network topology solving method in a data transmission time slot, completing the global optimization of the network topology of the idle time slot, and obtaining the final inter-satellite link network topology plan of the link establishment period, wherein the result is shown in figure 5.
The foregoing detailed description of the preferred embodiments of the invention has been presented. It should be understood that numerous modifications and variations could be devised by those skilled in the art in light of the present teachings without departing from the inventive concepts. Therefore, the technical solutions available to those skilled in the art through logic analysis, reasoning and limited experiments based on the prior art according to the concept of the present invention should be within the scope of protection defined by the claims.
Claims (9)
1. A satellite navigation system, comprising:
a satellite configured to perform the following actions:
determining a chain-building relation among satellites in each chain-building period and a visual relation between the satellites and a ground station according to a time range of inter-satellite link network topology planning; classifying the satellite nodes, and defining the satellite nodes as node satellites when the satellite is in the observation range of the ground station; when the satellite is not in the observation range of the ground station, defining the satellite as a non-node satellite;
dividing the time slot in a link establishing period into P complete combinations and Q residual time slots, wherein each complete combination comprises N time slots, N is more than Q and is not less than 0, and N is [ m ═ m2/m1]+1，[]Represents rounding up, m1Number of satellites as node, m2The number of non-node satellites;
step three, defining the 1 st to N-1 th time slots in each complete combination as data transmission time slots, and defining the Nth time slot as a measurement time slot; the definition of the Q remaining time slots is consistent with the 1 st to the Q th time slot definition in each complete combination; sequentially solving the network topology in each data transmission time slot in a link establishment period, and further solving the network topology in the measurement time slot;
step four, after the network topology solution of all the data transmission time slots and the measurement time slots in a link establishment period is completed, remaining satellite idle time slots are provided for expansion users outside the system, and inter-satellite link allocation with the expansion users outside the system is completed;
step five, after the inter-satellite link allocation of the user is completed and expanded outside the system, if the satellite is still in an idle state, the network topology of the idle time slot is globally optimized; and
a ground station configured to communicate with a non-nodal satellite over an inter-satellite link.
2. A method for topologically planning an inter-satellite link network of a satellite navigation system is characterized by comprising the following steps:
determining a chain-building relation among satellites in each chain-building period and a visual relation between the satellites and a ground station according to a time range of inter-satellite link network topology planning; classifying the satellite nodes, and defining the satellite nodes as node satellites when the satellite is in the observation range of the ground station; when the satellite is not in the observation range of the ground station, defining the satellite as a non-node satellite;
dividing the time slot in a link establishing period into P complete combinations and Q residual time slots, wherein each complete combination comprises N time slots, N is more than Q and is not less than 0, and N is [ m ═ m2/m1]+1，[]Represents rounding up, m1Number of satellites as node, m2The number of non-node satellites;
step three, defining the 1 st to N-1 th time slots in each complete combination as data transmission time slots, and defining the Nth time slot as a measurement time slot; the definition of the Q remaining time slots is consistent with the 1 st to the Q th time slot definition in each complete combination; sequentially solving the network topology in each data transmission time slot in a link establishment period, and further solving the network topology in the measurement time slot;
step four, after the network topology solution of all the data transmission time slots and the measurement time slots in a link establishment period is completed, remaining satellite idle time slots are provided for expansion users outside the system, and inter-satellite link allocation with the expansion users outside the system is completed;
and step five, after the inter-satellite link allocation of the user is completed and expanded outside the system, if the satellite is still in an idle state, performing global optimization on the network topology of the idle time slot.
3. The method for topologically planning the inter-satellite link network by using the satellite navigation system as claimed in claim 2, wherein the topology planning of the inter-satellite link network for planning all link establishment periods of the time range is sequentially completed according to the first step to the fifth step.
4. The method for topologically planning an inter-satellite link network for a satellite navigation system according to claim 2, wherein in the third step, the solving of the network topology in the data transmission time slot comprises:
defining a complete bipartite graph G (X, Y, E), wherein X and Y are point sets, E is an edge set, X represents a node satellite set, Y represents a non-node satellite set, and E represents all inter-satellite links with link establishment conditions between the node satellite set X and the non-node satellite set Y; and (3) solving the maximum matching problem of the bipartite graph G (X, Y, E), thereby completing the distribution of the inter-satellite links between the non-node satellite and the node satellite.
5. The method for topologically planning an inter-satellite link network for a satellite navigation system according to claim 2, wherein in the third step, the network topology solution in the measurement time slot comprises the following steps:
step 31, judging whether the idle state satellite of the current time slot reaches an observation PDOP value threshold;
step 32, extracting all satellite nodes which are in an idle state and do not reach a PDOP value threshold in the current ranging time slot to form a node set A, and meanwhile, sequencing the nodes in the set A from large to small according to the current observed PDOP value;
step 33, extracting the first satellite node a in the set A1Will be connected with the satellite node a1The satellite nodes which can build the chain form a set B, and all the satellite nodes in the set B are sequentially ordered according to the priority;
step 34, select the 1 st satellite in the set BStar node b1At satellite node a1And satellite node b1Planning inter-satellite link when satellite node a1And satellite node b1No longer in the idle state.
6. The method for topologically planning an inter-satellite link network in a satellite navigation system according to claim 5, wherein the inter-satellite link planning of all nodes in the current time slot is completed in sequence according to the steps 31 to 34, and the remaining satellite nodes without chain establishment are placed in an idle state.
7. The method according to claim 5, wherein in step 33, the priority definition is classified into 3 categories, and sequentially comprises, according to the order of decreasing importance:
the class 1 priority is based on the number of established links of the target satellite and the source satellite, is sorted from small to large according to the number of established links of the target satellite and the source satellite, and has the highest priority of the satellite node with the least number of established links of the source satellite;
the type 2 priority is based on the orbit type of the target satellite, the target satellites are classified according to the orbit type, the same-orbit target satellite located in the same orbit plane with the source satellite has low priority, and the different-orbit target satellite located in different orbit planes has high priority;
and the 3 rd type priority is based on the improvement degree of the target satellite on the PDOP value observed by the source satellite, the improvement values are sorted from large to small, and the target satellite with the maximum improvement value has the highest priority.
8. The method for topologically planning an inter-satellite link network for a satellite navigation system of claim 7, wherein the next priority is compared when the same class of priorities are in the same order.
9. The method for topologically planning the inter-satellite link network in the satellite navigation system according to claim 2, wherein in the fifth step, the global optimization comprises the following steps:
step 51, sequentially selecting all time slots in a link establishment period, and executing the following steps;
step 52, extracting the satellite nodes in the idle state in the current time slot, and solving according to a network topology solving method in a measurement time slot, wherein the observation PDOP value is not set at the moment;
step 53, dividing the rest satellite nodes in the idle state in the time slot into a node satellite set X and a non-node satellite set Y, if so, determining whether the rest satellite nodes in the time slot are in the idle state
Or
Switching to the next time slot for solving; otherwise, solving according to a network topology solving method in a data transmission time slot.
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