Inter-satellite reliable routing method based on fault domain model

Abstract

The invention provides an inter-satellite reliable routing method based on a fault domain model, and belongs to the technical field of satellite communication. The invention provides a centralized inter-satellite reliable routing method based on inter-satellite link attributes in order to solve the problems of transmission failure and routing interruption caused by the fact that inter-satellite links are easily influenced by space environments and man-made interference. The inter-satellite links are classified according to real-time states and failure reasons of the inter-satellite links, an initial topology model containing global network information is constructed, a boundary diffusion method is designed in combination with fault link boundary node states, and fault links are aggregated into blocks to form a fault domain topology model so as to limit a fault influence range. According to the method, the influence of the buffer queue capability, the link signal-to-noise ratio and the path length on routing is analyzed, a comprehensive link utility function is constructed to quantify the link quality, a multi-attribute detour path selection method is provided to solve the problem of load imbalance caused by a single path selection criterion, the system packet loss rate and the end-to-end delay are reduced, and the satellite network fault handling capability is improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of wireless communication and specifically relates to an inter-satellite reliable routing method based on a fault domain model. Background Art

[0002] In recent years, with the rapid growth of the number of users and the explosion of traffic brought by data services. At present, users have increasingly stringent requirements for communication reliability, stability, real-time performance, etc. Compared with traditional communication methods, satellite communication has excellent global coverage capabilities and high reliability and low latency communication characteristics. In particular, with the development of recyclable rocket technology and multi-satellite technology, the launch cost of satellites is gradually decreasing. Therefore, satellite communication is expected to become an important part of the next generation network. Inter-satellite routing technology can ensure reliable and efficient transmission of data between satellites, thereby enabling ground users to achieve global coverage communication through satellites. However, the high-speed movement of satellites and their spatial characteristics also bring a series of new problems to inter-satellite routing, such as dynamic topology, prone to failure, and limited resources. And unlike the ground, satellite failures will become difficult to maintain and repair. Therefore, it is necessary to focus on the reliability of routing, starting from the analysis of network fault information and routing algorithm design, and conduct a more in-depth study on inter-satellite reliable routing strategies.

[0003] SDN (Software Defined Network) technology has the characteristics of decoupling the forwarding plane from the control plane. Its main advantages are flexibility, programmability and logical centralization. SDN technology is conducive to the centralized management of satellite nodes to cope with the management challenges brought by the current giant constellations. At the same time, SDN technology can also be applied to inter-satellite routing. Due to the special management method of SDN technology, the original distributed routing solution is no longer suitable for the SDN architecture. Therefore, the routing solution based on SDN can realize the centralized management of nodes and reduce the probability of satellite node failure to a certain extent.

[0004] According to the existing research on intersatellite routing methods, they can be divided into two categories according to the way they handle dynamic topology: dynamic routing algorithms and static routing algorithms. The former is to flood routing information including fault information to the global network, and then design routing methods based on the real-time dynamic monitoring information in the network. However, in the context of the current huge constellation, simply flooding the information to the global network will greatly increase the transmission delay. In order to solve this problem, the static routing algorithm divides the routing into multiple "snapshots" of topological information under a certain time slot. Since the network topology basically does not change within the divided time slice, the path calculation can be performed through the static routing algorithm. This method perfectly obtains the conventional network topology change information brought by satellite movement, and it no longer needs to be flooded. However, it is not sensitive enough to sudden topological changes in the network, and it also causes excessive routing overhead.

[0005] The present invention proposes a reliable inter-satellite routing method based on a fault domain model. Considering the problem of excessive flooding delay of dynamic routing, the present invention adopts a static routing method to solve the dynamic topology problem, designs a multi-layer network SDN architecture to solve the management problem of satellite nodes, and facilitates the calculation of static routing algorithms. In view of the problem that static routing is insensitive to sudden topology changes, the present method first establishes a virtual topology based on logical addresses, and then designs a routing fault model based on the idea of ​​a fault block model to reduce the waste of available nodes to manage topology information, and proposes a path selection method based on this model. The method segments the routing process according to routing requirements, and in terms of path selection, the path length, signal-to-noise ratio and queue buffer capacity are weighted to obtain a link utility function to select the routing path, which can effectively avoid possible load imbalance problems and reduce packet loss rate and average end-to-end delay. Summary of the invention

[0006] The present invention aims to solve the above problems of the prior art. A distributed user association method is proposed to ensure user mobility and latency requirements. The method takes into account the characteristics and needs of the user, and also takes into account the characteristics of heterogeneous networks, and obtains user association results by a distributed algorithm. The technical solution of the present invention is as follows:

[0007] A reliable inter-satellite routing method based on a fault domain model comprises the following steps:

[0008] S1: Establishing a virtual topology based on logical addresses according to the initial topology information of the satellite network;

[0009] S2: Re-divide the nodes into faulty nodes, boundary nodes, unreachable nodes, unreliable nodes and available nodes according to the node status, then traverse the faulty nodes to obtain the boundary node status, and then merge the faulty nodes in the boundary node set with the original faulty nodes, unreliable nodes and unreachable nodes surrounded by the faulty nodes to obtain the faulty node set F{Ni,j} and the boundary node set B{N i,j}, the available node set S{N i,j}Through the total set and the fault node set F{N i,j} and the boundary node set B{N i,j}, obtain the location of the source node and the destination node, calculate the detour priority Round, the boundary initial node B s and the border destination node B d Location;

[0010] S3: Determine whether the shortest path between the source node and the destination node is blocked by the fault area. If it is blocked, execute the fault domain-based routing algorithm; if it is not blocked, execute the conventional routing algorithm;

[0011] S4: Execute the fault domain routing algorithm, calculate the signal-to-noise ratio utility function U(s), link length utility function U(l), buffer queue utility function U(b), and comprehensive utility function U(x) according to the network information, and calculate the optimal routing path.

[0012] Furthermore, the specific process of step S1 establishing a virtual topology based on a logical address according to a satellite network is as follows:

[0013] First, the topological relationship of the satellite network is shown in the figure express, represents the set of satellites, ε={l 11 , l 12 ,...,l ij} represents the set of interconnections between these satellites, and the connection relationship is represented by an association matrix. The elements in the matrix are 0 for a link and 1 for no link;

[0014] Secondly, a virtual topology model will be established based on the constellation topology, giving each satellite a logical address, which is fixed on the satellite; the logical topology of the satellite will change with the movement of the satellite; the logical address of satellite S is (i, j), and N i,j represents the jth satellite node on the i-th orbital plane, i = 0, ..., M-1; j = 0, ..., N-1; then the instantaneous topology of the satellite network is determined by the actual position of a satellite and the relative position obtained by the hello data packet.

[0015] Furthermore, the step S2 specifically includes:

[0016] The set of faulty nodes F{N i,j} represents the location set of all failed nodes and unreachable nodes;

[0017] The boundary node set B{N i,j} is composed of available nodes adjacent to the faulty node, which is used to represent the boundary of the faulty node; at the same time, the initial node in the boundary detour process is called the boundary initial node B s The node where the detour ends is named the boundary destination node B d ;

[0018] Define the detour priority Round(0,1) as a judgment condition. Round is calculated directly by which direction has the smaller number of hops. A value of 0 represents clockwise, and a value of 1 represents counterclockwise.

[0019] Furthermore, the routing algorithm step based on the fault domain in step S3 specifically includes:

[0020] Based on the relative positions of the source node and the destination node, the routing paths of source-boundary initial, boundary initial-boundary destination, and boundary destination-destination are calculated segment by segment in combination with the comprehensive link utility function. The three segments are integrated to obtain the most reliable routing path blocked by the fault domain.

[0021] Furthermore, the signal-to-noise ratio utility function U(s) in step S4 specifically includes:

[0022] During laser link transmission, the signal-to-noise ratio is mainly affected by free space propagation loss, which can be quantified as follows:

[0023]

[0024] Among them, y ij is the final signal, h ij is the link loss factor, n ij is Gaussian white noise; G is the source node transmission power, L ij is the distance, γ is the path loss index; in formula (1), SNR ij (t) is the signal-to-noise ratio of the link, N0 is Gaussian white noise;

[0025] When the signal-to-noise ratio of the transmission process is lower than the signal-to-noise ratio of the receiving threshold α, data transmission will not be possible. Therefore, the probability of an interruption event is derived as follows:

[0026]

[0027] Then the probability of data packet interruption between satellites i and j is derived as:

[0028]

[0029] In order to ensure the transmission efficiency of data packets, the utility function U(s) of the signal-to-noise ratio is defined as the probability of successful transmission of the data packet, expressed as:

[0030] U(s)=1-P r{SNR ij (t)<α} (4).

[0031] Furthermore, the path length utility function U(l) in step S4 specifically includes:

[0032] The shortest path can be calculated using the following formula:

[0033] MinL=MinL v +MinL h . (5)

[0034] Where L v represents the in-plane ISL length, L h represents the inter-plane ISL length, which is calculated by the following formulas (6)-(8):

[0035]

[0036] L h =δ×cos(lat) (7)

[0037]

[0038] Among them, lat represents the latitude of the inter-plane ISL. The satellite network has M polar orbit planes, and each polar orbit plane has N satellites. The angular distance between two adjacent planes is 360° / (2×M), and the angular distance between two adjacent satellites in the same orbital plane is 360° / N.

[0039] The path length utility formula can be calculated using the path length:

[0040] U(l)=MinL (9).

[0041] Furthermore, in step S4, the buffer queue utility function U(b) is specifically:

[0042] According to queuing theory, the packet arrival rate follows a Poisson distribution with an average rate of λ. A(t) represents the number of packets arriving in period t. The probability function of A(t) = k is:

[0043]

[0044] The service time of each message obeys an independent but identical distribution function, which is set to B(t). Define v n is the processing time of the nth data packet,

[0045]

[0046] V nrepresents the independent processing time of a data packet, D(t) represents the number of data packets processed by the satellite within time t;

[0047] D(t)=max{n:V n ≤t} (12)

[0048] P(D(t)=n)=B n (t)-B n+1 (t) = C n (t) (13)

[0049] Where B n (t) is the n-fold convolution of B(t), C n (t) represents the probability function that the number of packets processed by the satellite in time t is equal to n, which can be calculated by (13). Then, at time t, the packet length X(t) is expressed as:

[0050] X(t)=m+A(t)-D(t) (14)

[0051] Where m is the number of remaining packets at time t, then the processing probability p of the current data queue X(t) is obtained m,k (t), where j represents the number of datagrams processed by the satellite in the current data queue;

[0052]

[0053] The buffer queue can characterize the congestion handling capability of the link, so the ISL utility function of the buffer queue is:

[0054] U(b)=p m,k (t) (16).

[0055] Furthermore, the comprehensive link utility function U(x) in step S4 is specifically:

[0056]

[0057] Where ω represents the weight of each utility function, and formula (15) satisfies the following two constraints:

[0058]

[0059] The advantages and beneficial effects of the present invention are as follows:

[0060] The present invention mainly proposes a reliable intersatellite routing method based on a fault domain model for the specific problems of dynamic topology and communication process failures in the intersatellite routing process. The main innovation of the present invention is to propose a topology model that can more effectively describe fault information in static routing, and based on this model, to propose a routing method that can still achieve high reliability at a low cost when a node in the satellite network fails, thereby ensuring the continuity of communication. The existing research focuses on how to design and implement a highly reliable routing algorithm and select a simple single factor such as the shortest path or the minimum number of hops to select the routing path. Therefore, the reliable routing method based on the fault model proposed in the present invention is not easy for existing technicians to think of. Furthermore, the present invention invents a routing fault model and a highly reliable intersatellite routing algorithm based on the characteristics of the current low-orbit satellite constellation, so that a reliable routing design with the characteristics of the low-orbit constellation can be generated. Therefore, the present invention is unique and creative. Since the space environment in which the satellite is located is easily affected by solar activities, malicious attacks and other satellites, failures in the satellite communication process occur from time to time. The present invention fully considers the factors that cause failures and combines them with the topological model, completes the design of a routing failure model based on the idea of ​​fault blocks, fully analyzes the status and parameters of each satellite node and intersatellite link, and develops a highly reliable routing algorithm. In existing studies, the research model set by researchers is too idealistic and does not consider the variable constraints in extreme scenarios. Therefore, the present invention has the characteristics of creativity and difficulty in implementation in terms of solution. By building a simulation platform for constellation operation and inputting the orbital parameters and link parameters of the constellation operation, reliable transmission of routing is achieved. At the same time, according to the actual situation, the intersatellite routing is better specialized. BRIEF DESCRIPTION OF THE DRAWINGS

[0061] Figure 1 The present invention provides a routing fault model based on a virtual network in a preferred embodiment;

[0062] Figure 2 A network scenario diagram based on software-defined networking built for the present invention;

[0063] Figure 3 This is a flow chart of the fault domain-based inter-satellite reliable routing algorithm described in the present invention. DETAILED DESCRIPTION

[0064] The following will describe the technical solutions in the embodiments of the present invention in detail in conjunction with the accompanying drawings in the embodiments of the present invention. The described embodiments are only part of the embodiments of the present invention.

[0065] The technical solution of the present invention to solve the above technical problems is:

[0066] A reliable inter-satellite routing method based on SDN is proposed. The process of this method is as follows Figure 2 As shown in the figure, first, under the premise that the static routing virtual topology model has been obtained, according to the status and reachability of the nodes in the satellite network, the satellite nodes are divided into three subsets: available nodes, faulty nodes and faulty boundary nodes according to the model to construct a network topology model. Then, based on the idea of ​​segmented routing, a detour routing method is designed and implemented. At the same time, this method assists in routing path selection by introducing a comprehensive utility function of multiple elements such as link signal-to-noise ratio, path length and buffer queue, and finally realizes reliable inter-satellite routing. This method reduces the waste of available nodes in the satellite network and reduces the packet loss rate and average end-to-end delay of the inter-satellite link. The specific steps are as follows:

[0067] Step 101: Establishing a virtual topology based on a logical address according to a satellite network;

[0068] Step 102: Establish an inter-satellite routing fault model based on node status and reachability, traverse the faulty node to obtain its boundary node status, and then integrate it with the original faulty node and the unreachable nodes surrounded by the faulty node to obtain the faulty node set F{N i,j}, boundary node set B{N i,j}, the available node set S{N i,j} can be calculated by using the total set and the difference set of the above two nodes to obtain the positions of the source node and the destination node, and calculate the detour priority Round and the boundary initial node B s and the border destination node B d Location;

[0069] Step 103: Determine whether the shortest path between the source node and the destination node is blocked by the fault area. If so, execute a routing algorithm based on the fault domain. If not, directly return the shortest path.

[0070] Step 104: Execute the fault domain routing algorithm to calculate the signal-to-noise ratio utility function U(s), the link length utility function U(l), the buffer queue utility function U(b), and the comprehensive utility function U(x) according to the network information, and calculate the optimal routing path;

[0071] The models involved in the present invention are as follows:

[0072] (1) Network model:

[0073] The main scenario of the present invention is a multi-layer satellite-ground fusion network based on SDN, which can be divided into two parts: the space segment and the ground segment as shown in the figure. The space segment includes three parts: LEO satellite, MEO satellite and GEO satellite, and the ground end includes SDN control center, users and base stations. At the logical level, the ground, MEO satellite and GEO satellite are the control layer, on which the SDN controller is deployed. The low-orbit satellite serves as the data plane and has only a simple forwarding function. The MEO satellite serves as the secondary control layer, which can collect and store the LEO satellite topology data (including historical data) within its coverage area, and finally hand it over to the high-orbit satellite for unified management. At the same time, the GEO satellite will transmit the collected constellation information back to the ground, so the computing management module of the GEO satellite should be software-based to facilitate interaction with the ground.

[0074] (2) Routing Failure Model:

[0075] The fault model designed by the present invention is as follows Figure 1 As shown in the figure, points represent satellite nodes and edges represent connection relationships. This method divides nodes into five types according to node status and connection relationships: available nodes, faulty nodes, unreachable nodes, unreliable nodes, and boundary nodes.

[0076] The systems, devices, modules or units described in the above embodiments may be implemented by computer chips or entities, or by products with certain functions.

[0077] It should also be noted that the terms "include", "comprises" or any other variations thereof are intended to cover non-exclusive inclusion, so that a process, method, commodity or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, commodity or device. In the absence of more restrictions, the elements defined by the sentence "comprises a ..." do not exclude the existence of other identical elements in the process, method, commodity or device including the elements.

[0078] The above embodiments should be understood to be only used to illustrate the present invention and not to limit the protection scope of the present invention. After reading the contents of the present invention, technicians can make various changes or modifications to the present invention, and these equivalent changes and modifications also fall within the scope defined by the claims of the present invention.

Claims

1. A reliable inter-satellite routing method based on a fault domain model, characterized in that: The steps include: S1: Establishing a virtual topology based on logical addresses according to the initial topology information of the satellite network; S2: Re-divide the nodes into faulty nodes, boundary nodes, unreachable nodes, unreliable nodes and available nodes according to the node status, then traverse the faulty nodes to obtain the boundary node status, and then merge the faulty nodes in the boundary node set with the original faulty nodes, unreliable nodes and unreachable nodes surrounded by the faulty nodes to obtain the faulty node set F{N i,j } and the boundary node set B{N i,j }, the available node set S{N i,j }Through the total set and the fault node set F{N i,j } and the boundary node set B{N i,j }, obtain the location of the source node and the destination node, calculate the detour priority Round, the boundary initial node B s and the border destination node B d Location; S3: Determine whether the shortest path between the source node and the destination node is blocked by the fault area. If it is blocked, execute the fault domain-based routing algorithm; if it is not blocked, execute the conventional routing algorithm; S4: Execute the fault domain routing algorithm, calculate the signal-to-noise ratio utility function U(s), link length utility function U(l), buffer queue utility function U(b), and comprehensive utility function U(x) according to the network information, and calculate the optimal routing path criterion.

2. The inter-satellite reliable routing method based on the fault domain model according to claim 1, characterized in that: The specific process of step S1 establishing a virtual topology based on a logical address according to a satellite network is as follows: First, the topological relationship of the satellite network is shown in the figure express, represents the set of satellites, ε={l 11 , l 12 ,...,l ij } represents the set of interconnections between these satellites, and the connection relationship is represented by an association matrix. The elements in the matrix are 0 for a link and 1 for no link; Secondly, a virtual topology model will be established based on the constellation topology, giving each satellite a logical address, which is fixed on the satellite; the logical topology of the satellite will change with the movement of the satellite; the logical address of satellite S is (i, j), and N i,j represents the jth satellite node on the i-th orbital plane, i = 0, ..., M-1; j = 0, ..., N-1; then the instantaneous topology of the satellite network is determined by the actual position of a satellite and the relative position obtained by the hello data packet.

3. The inter-satellite reliable routing method based on the fault domain model according to claim 1, characterized in that: The step S2 specifically includes: The set of faulty nodes F{N i,j } represents the location set of all failed nodes and unreachable nodes; The boundary node set B{N i,j } is composed of available nodes adjacent to the faulty node, which is used to represent the boundary of the faulty node; at the same time, the initial node in the boundary detour process is called the boundary initial node B s The node where the detour ends is named the boundary destination node B d ; Define the detour priority Round(0,1) as a judgment condition. Round is calculated directly by which direction has the smaller number of hops. A value of 0 represents clockwise, and a value of 1 represents counterclockwise.

4. The inter-satellite reliable routing method based on the fault domain model according to claim 1, characterized in that: The routing algorithm steps based on the fault domain in step S3 specifically include: Firstly, based on the relative positions of the source node and the destination node, the routing paths of source-boundary initial, boundary initial-boundary destination, and boundary destination-destination are calculated segmentally in combination with the comprehensive link utility function. The routing path of boundary initial-boundary destination is calculated according to the detour priority. Finally, the three segments are integrated to obtain the most reliable routing path blocked by the fault domain.

5. The inter-satellite reliable routing method based on the fault domain model according to claim 1, characterized in that: The signal-to-noise ratio utility function U(s) in step S4 specifically includes: During laser link transmission, the signal-to-noise ratio is mainly affected by free space propagation loss, which can be quantified as follows: Among them, y ij is the final signal, h ij is the link loss factor, n ij is Gaussian white noise; G is the source node transmission power, L ij is the distance, γ is the path loss index; in formula (1), SNR ij (t) is the signal-to-noise ratio of the link, N0 is Gaussian white noise; When the signal-to-noise ratio of the transmission process is lower than the signal-to-noise ratio of the receiving threshold α, data transmission will not be possible. Therefore, the probability of an interruption event is derived as follows: Then the probability of data packet interruption between satellites i and j is derived as: In order to ensure the transmission efficiency of data packets, the utility function U(s) of the signal-to-noise ratio is defined as the probability of successful transmission of the data packet, expressed as: U(s)=1-P r {SNR ij (t)<α} (4)。 6. The inter-satellite reliable routing method based on the fault domain model according to claim 5, characterized in that: The path length utility function U(l) in step S4 specifically includes: The shortest path can be calculated using the following formula: MinL=MinL v +MinL h . (5) Where L v represents the in-plane ISL length, L h represents the inter-plane ISL length, which is calculated by the following formulas (6)-(8): L h =δ×cos(lat) (7) Among them, lat represents the latitude of the inter-plane ISL. The satellite network has M polar orbit planes, and each polar orbit plane has N satellites. The angular distance between two adjacent planes is 360° / (2×M), and the angular distance between two adjacent satellites in the same orbital plane is 360° / N. The path length utility formula can be calculated using the path length: U(l)=MinL (9).

7. The inter-satellite reliable routing method based on the fault domain model according to claim 6, characterized in that: In step S4, the buffer queue utility function U(b) is specifically: According to queuing theory, the packet arrival rate follows a Poisson distribution with an average rate of λ. A(t) represents the number of packets arriving in period t. The probability function of A(t) = k is: The service time of each message obeys an independent but identical distribution function, which is set to B(t). Define v n is the processing time of the nth data packet, V n represents the independent processing time of a data packet, D(t) represents the number of data packets processed by the satellite within time t; D(t)=max{n:V n ≤t} (12) P(D(t)=n)=B n (t)-B n+1 (t)=C n (t) (13) Where B n (t) is the n-fold convolution of B(t), C n (t) represents the probability function that the number of packets processed by the satellite in time t is equal to n, which can be calculated by (13). Then, at time t, the packet length X(t) is expressed as: X(t)=m+A(t)-D(t) (14) Where m is the number of remaining packets at time t, then the processing probability p of the current data queue X(t) is obtained m,k (t), where j represents the number of datagrams processed by the satellite in the current data queue; The buffer queue can characterize the congestion handling capability of the link, so the ISL utility function of the buffer queue is: U(b)=p m,k (t) (16)。 8. The inter-satellite reliable routing method based on the fault domain model according to claim 7, characterized in that: The comprehensive link utility function U(x) in step S4 is specifically: Where ω represents the weight of each utility function, and formula (15) satisfies the following two constraints:

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