CN101299713A - Method for setting multilayer satellite network system route - Google Patents

Abstract

The present invention relates to a method for setting multilayer satellite network system route, including steps of: 1. setting parameters for the network initialization; 2. fixing a time, solving satellite orbit parameters in the interval of time, calculating the location coordinates of the satellite and the length of the link between stars, and establishing a network topological structure; 3. calculating the load of link between stars of the multi-layer satellite network; 4. calculating the process and exchange time delay on stars according to the queuing theory; 5. searching source satellite and object satellite of each satellite layer; 6. selecting the satellite layer for transporting services according to the communication service instruction requirement and network states, and searching an optimum route according to routing algorithm. Relative to traditional stationary orbit satellite, the present invention has small transmission delay, and high validity. The system has advantages of more flexible routing, effective guaranty of service quality, multiple replaceable chain circuits, stronger survivability, a capacity of processing and exchanging on star, optical or microwave links between stars, and capability of providing wideband synthetic service for users in global scope.

Description

A multi-layer satellite network system routing setting method

technical field

The invention belongs to the field of deep space communication, and in particular relates to a multilayer satellite network system routing setting method.

Background technique

Early satellite communications often used a single geostationary orbit satellite with an orbital altitude of about 35,786 kilometers and an orbital inclination of 0 degrees. It was located at a certain longitude position above the equator and was stationary relative to the ground. Geostationary orbit satellites have a high orbit and a large coverage area, but due to the large communication distance between the satellite and the ground, the link is easily damaged, and it does not support low-power users such as ground handsets. At the same time, because the geostationary orbit satellite orbit has an inclination angle of 0 degrees, it cannot cover the polar regions, and the communication angle in high latitude regions is small, and the communication quality is difficult to guarantee. The emergence of satellite inter-satellite link technology makes geostationary orbit satellites form a network, and the satellites can communicate. The design method of the geostationary satellite network is relatively simple. It is only necessary to determine how many satellites can form the network and the longitude position of the satellite. Other parameters are relatively determined.

The medium-orbit satellites are located in the orbit between the two Van Allen belts. The constellation is generally composed of more than a dozen satellites, and the visible time of a single satellite is 1 to 2 hours. As a compromise between geostationary orbit satellites and low-orbit satellites, the double-hop transmission delay of medium-orbit satellites is greater than that of low-orbit satellites. The delay performance of the satellite network may be better than that of the low-orbit satellite network. At the same time, compared with low-orbit satellites, medium-orbit satellites have a low switching probability and a small Doppler effect. The orbit control system and antenna tracking system are simplified, and generally can obtain a communication angle of 20 to 30 degrees.

Low-orbit satellites are distributed in circular or elliptical orbits ranging from 500 to 2,000 kilometers, and a satellite communication network generally consists of dozens of satellites. The visibility time of a single satellite is short, requiring beam switching and satellite switching. Low-orbit satellites have many advantages, because the orbit is low, the performance of the inter-satellite link is superior, and the transmission delay is small. At the same time, the application of small satellite technology makes the satellite smaller and easier to launch. However, the network construction period composed of low-orbit satellites is long, the space control system is relatively complex, and the system investment is huge. At the same time, a large number of gateway stations need a fast tracking and targeting system, and the Doppler effect needs to be considered. The satellite orbit is low, and the communication elevation angle is about 10 degrees. Because of the rapid change of the elevation angle, the signal transmission path is different.

Considering the orbits of polar orbits or near-polar orbits such as π-shaped constellations, there is a "gap" between the opposite-moving orbits, and the satellites on both sides of the gap cannot establish an inter-orbital link because of their relative motion; at the same time, the inter-orbital link is over the polar regions It must be closed, because over the polar regions, the orbits of adjacent satellites cross, and the inter-satellite distance changes rapidly, making it impossible to establish an inter-satellite link.

In addition, during the research process, it was found that the single-layer satellite network, especially the low-orbit (LEO: Low Earth Orbit) and medium-orbit (MEO: Medium Earth Orbit) satellite network, the space distance between the two satellites is very close, but because there is no inter-satellite link (ISL: Inter-Satellite Link) direct connection makes it impossible to communicate directly. The communication must be completed through satellite paths established by several ISLs. This not only fails to meet the communication service instructions (QoS: Quality of Service), but also wastes a lot of system and satellite resources. resources, and even cause link congestion.

In order to effectively solve the above technical problems, many research institutions are conducting satellite interlayer link tests. In the European SILEX test, the LEO satellite SPOT IV and the GEO satellite Artemis communicate at a rate of 50Mbps through a 0.8μm inter-satellite link. The inter-satellite communication experiment with Japan's OICETS satellite is completed. The ISL of the two experiments is the optical link from LEO to GEO satellite. The United States has also conducted a similar ISL experiment. Other plans such as Motorola combine the Celestri low-orbit satellite system with GEO satellites to form a hybrid satellite network. 13 LEO satellites and 6 MEO satellites together form the Rostelesat constellation. GESN, GNSS/Galileo and West systems are composed of different numbers of MEO/ GEO satellite composition, etc.

Multi-layer satellite networks (MLSN: Multi layer satellite networks) became a research hotspot in the late 1990s. Kimura proposed a double-layer (LEO and MEO) satellite constellation, comparing the difference between the polar orbit and the inclined orbit constellation. Through the method of multi-coverage and increasing the elevation angle, the reliability requirements of communication are guaranteed, but the number of satellites is huge.

Contents of the invention

In order to solve the technical problems existing in the prior art that the satellite network system is huge, causing a large amount of system and on-board resources to be wasted, the time extension during the transmission process, and easily causing link congestion, etc., the present invention provides a multi-layer satellite network system routing design Determine the method.

The solution adopted by the present invention to solve the problems of the prior art is to provide a multi-layer satellite network system routing setting method, the routing setting method includes steps: the first step, setting parameters, and performing network initialization; the second step, Fix a time t _k , in this time interval Δt, solve the satellite orbit parameters, calculate the satellite position coordinates and the length of the inter-satellite link, and establish the network topology; the third step is to calculate the multi-layer satellite according to the set business model The inter-satellite link load of the network. The fourth step is to calculate the delay of on-board processing and exchange according to the queuing theory; the fifth step is to find the source satellite and target satellite in each satellite layer according to the ground source target position; The state selects the satellite layer of the transmission service, and finds the optimal path according to the routing algorithm.

According to a preferred embodiment of the present invention: the parameters set in the first step include: the number of layers of the multi-layer satellite network, the number of satellites in each layer, the number of inter-satellite links, each satellite orbit type, orbit height, Orbital inclination and number of orbits.

According to a preferred embodiment of the present invention: the third step further includes sub-steps: 1. Under the non-uniform distribution model, the population density is divided into 5 levels in consideration of the differences in user distribution between land and sea, desert and plain , use numbers to represent the population density in each region; 2. Divide the earth's surface into 48 parts, adopt the method of dividing parallel to the latitude and oblique to the meridian, and the 8 oblique lines are 52 degrees to the latitude. Divide the longitude 360 degrees into 8 parts and the latitude into 6 parts; set up a ground station in each area, the ground stations are located at 15 degrees north and south latitude, 45 degrees and 68 degrees, the number is 48; adopt the maximum elevation angle access scheme Access; 3. Under the statistical distribution model, consider the difference in user distribution density, the location and density difference of the source and target of the call, and obtain the channel occupancy of each inter-satellite link in the network.

According to a preferred embodiment of the present invention: the fourth step further includes sub-steps: one, according to the queuing theory, each inter-satellite link can be regarded as a single service window mixed system queuing model M/M/l/m, Each inter-satellite link only contains a single service window, and the interval between arrivals of "customers" obeys a negative exponential distribution with a parameter of β; the service time is a negative exponential distribution with a parameter of μ; each inter-satellite link has m queuing capacity . When there are already m data packets in the system, new data packets will no longer enter the queue, there is: ρ=β/μ; 2. The average waiting time delay of data packets is $W=\frac{1}{\mathrm{\μ}\&Center\; Dot;(1-\mathrm{\ρ})}-\frac{m\&Center\; Dot;{\mathrm{\ρ}}^m}{\mathrm{\μ}\&Center\; Dot;(1-{\mathrm{\ρ}}^m)}.$

According to a preferred embodiment of the present invention: the routing algorithm in the sixth step is the FBellman-Ford routing algorithm.

According to a preferred embodiment of the present invention: the sixth step specifically includes sub-steps: six steps, the default service is the low-orbit layer in the multi-layer satellite network system, if the medium-orbit source satellite and the target satellite are the same, And the low-orbit source satellite and the target satellite are different, execute steps six and four; if the geostationary orbit source satellite and the target satellite are the same, and the low-orbit and medium-orbit source satellites and target satellites are different, execute steps six and five; otherwise, execute steps Step 62; Step 62: If the low-orbit layer path contains the number of inter-satellite links less than or equal to the low-orbit threshold of the inter-satellite link, perform step six and step three; if the low-orbit layer path contains the number of inter-satellite links Greater than the low-orbit threshold of the inter-satellite link, and the number of inter-satellite links contained in the mid-orbit layer path is less than or equal to the mid-orbit threshold of the inter-satellite link, perform steps 6 and 4; otherwise, perform steps 6 and 5; step 6 and 3: establish The optimal communication path at the low-orbit satellite layer to complete the transmission task; the sixth and fourth steps: establish the optimal communication path at the medium-orbit satellite layer to complete the transmission task; the sixth and fifth steps: establish the optimal communication path at the geostationary satellite layer to complete the transmission task; six Step six: Statistical parameters of the multi-layer network in the multi-layer satellite network system, and analyze network performance; Step six and seven: update the time interval, complete the calculation of the new routing table and complete the satellite handover.

According to a preferred embodiment of the present invention: the Bellman-Ford routing algorithm that described step 63 steps, 64 steps and 65 steps are applied to, this algorithm includes sub-steps: Step 1: make the T of all non-starting nodes in the network The label value is ∞, that is, T (i)=∞; the P label of the initial node is 0, that is, P (s)=0; Step 2: take the new P label as the initial node i, and check that i is the beginning Whether there is [P(i)+d(i,j)]<P(j) or [P(i)+d(i,j)]<T(j) for each terminal j of the edge of the node, if it exists , execute step 3, otherwise keep the original label; Step 3: Change the T label or P label at point j to a new T label T(j)=P(i)+d(i, j) or T(i) +d(i,j). Take the minimum value of the existing T-labeled points in the network, set it as a new P-labeled point, and repeat Step 2; Step 4: When all nodes in the network are P-labeled points, the algorithm ends.

According to a preferred embodiment of the present invention: the characteristic parameters that need to be counted in the six or six steps include: the memory usage percentage of each satellite node, the length of the inter-satellite link and the blocking probability.

The beneficial effects of the present invention are: compared with traditional geostationary orbit (GEO: Geostationary Earth Orbit) satellites, a global coverage network is formed by low-orbit (LEO: Low Earth Orbit) and medium-orbit (MEO: Medium Earth Orbit) satellites, and transmission delay Small hours, high effectiveness. Satellites have on-board processing and switching capabilities, and inter-satellite microwave or optical links can provide broadband integrated services to users around the world, effectively guaranteeing service quality, and the path selection is more flexible, and there are many replaceable links. The anti-destroy performance is stronger.

Description of drawings

Figure 1. Schematic diagram of the coverage slot structure of polar orbit or near polar orbit constellations;

Figure 2. Schematic diagram of the intersecting relationship between adjacent orbits of polar orbit or near-polar orbit constellations over the polar regions;

Fig. 3. Schematic diagram of the shortest path between the low-orbit satellite 11 and the low-orbit satellite 54 in the Walker delta constellation;

Figure 4. Schematic diagram of orbital parameters in the constellation;

Fig. 5. a kind of multi-layer satellite network system structure schematic diagram in the multi-layer satellite network system of the present invention and route setting method thereof;

Fig. 6. Schematic diagram of the spatial structure of the multi-layer satellite network system of the present invention;

Figure 7. Schematic diagram of the mathematical model for satellite inter-satellite link calculation;

Figure 8. Schematic diagram of the relationship between the average delay and the number of inter-satellite links in a multi-layer satellite network;

Figure 9. Schematic diagram of the normalized link load of the multi-layer satellite network changing with the channel capacity of the inter-satellite link;

Figure 10. Schematic diagram of normalized link load variation with network traffic in multi-layer satellite network;

Figure 11. Schematic diagram of the normalized link load over time in a multi-layer satellite network;

Figure 12. Schematic diagram of packet loss rate changing with average packet length;

Figure 13. Schematic diagram of the change of the comprehensive link weight of the multi-layer satellite network over time;

Figure 14. Distribution density map of multi-layer satellite network users;

Fig. 15 is a flow chart of a routing setting method in a multi-layer satellite network system and its routing setting method according to the present invention.

Detailed ways:

Below in conjunction with accompanying drawing and specific embodiment the present invention is described in further detail:

A key point of the satellite network is to develop a special satellite network routing algorithm to adapt to the dynamic characteristics of the satellite network. With the rapid development of the Internet, a seamless routing strategy is needed in the satellite network. Like the terrestrial network, there are IP switches on the satellite, which can transport IP packets independently, and the switches on the satellite are connected through ISL. The packet switching routing strategy based on the non-geostationary orbit satellite system has been widely studied, but because the satellite and the ground users are constantly moving relative to each other, the length of the ISL is constantly changing, the distribution of the ground users is uneven, and the traffic volume on the ISL is very different. From the perspective of ensuring the quality of service for users, or from the perspective of system maintainers optimizing network resources, establishing an effective multi-layer satellite network system and setting its routing is essential for the ISL backbone network.

Low-orbit, medium-orbit and geostationary-orbit satellites are divided according to orbital heights and have their own characteristics. For a long time, the advantages and disadvantages of satellite networks built with various satellites have also been compared and weighed to support different service quality requirements. Satellite communication networks constructed by low-orbit satellites and medium-orbit satellites have been operating around the earth. The establishment of inter-satellite links has made communication between satellites a reality, forming a real network, such as Iridium and Milstar-2 satellites network. The single-layer satellite network built by various satellites, especially the geostationary satellite network with a high orbital altitude, has too high communication delay indicators, and the multi-layer satellite network is conducive to solving the contradiction between switching probability and delay; In a single-layer satellite network, in order to achieve seamless global coverage, polar-orbit and near-polar-orbit constellations are usually used, which will result in increased inter-satellite link shutdown, switching probability, and blocking probability. Multi-layer satellites Each layer in the network complements each other, and can achieve global seamless coverage on the basis of inclined orbits, avoiding the above problems; the single-layer satellite network has poor invulnerability, and the single-layer satellite network can be used in the event of damage to satellites or inter-satellite links. It is not easy to find an alternative path that meets the requirements of the original communication indicators, and there are many backup links that can be replaced in the multi-layer satellite network, which will not cause a significant decline in communication quality; moreover, the single-layer satellite network, especially the low-orbit satellite network It is difficult to design a network satellite-borne tracking and targeting system, because low-orbit satellite networks often use polar orbits. In the multi-layer satellite network, through the relay of medium-orbit and geostationary-orbit satellites, the satellite network does not need to maintain the inter-satellite link between the reverse orbits in the low-orbit constellation, and can even use inclined orbits to realize the low-orbit satellite network, reducing Requirements for the spaceborne tracking and targeting system.

The present invention provides a multi-layer satellite network system routing setting method. The routing setting method includes the steps: the first step, setting parameters, and performing network initialization; the second step, fixing a time t _k , at the In the time interval Δt, solve the satellite orbit parameters, calculate the satellite position coordinates and the length of the inter-satellite link, and establish the network topology; the third step is to calculate the inter-satellite link load of the multi-layer satellite network according to the set business model. The fourth step is to calculate the delay of on-board processing and exchange according to the queuing theory; the fifth step is to find the source satellite and target satellite in each satellite layer according to the ground source target position; The state selects the satellite layer of the transmission service, and finds the optimal path according to the routing algorithm.

Wherein, the parameters set in the first step include: the number of layers of the multi-layer satellite network, the number of satellites in each layer, the number of inter-satellite links, the orbit type of each satellite, the orbit height, the orbit inclination, and the number of orbits. The third step further includes sub-steps: 1. Under the non-uniform distribution model, taking into account the differences in the distribution of land and sea, desert and plain users, the population density is divided into 5 levels, and the number of people in each area is represented by numbers. Population density; 2. Divide the earth's surface into 48 parts, adopt the division method parallel to the latitude and inclined to the meridian, and the 8 oblique lines are 52 degrees to the latitude. Divide the longitude 360 degrees into 8 parts and the latitude into 6 parts; set up a ground station in each area, the ground stations are located at 15 degrees north and south latitudes, 45 degrees and 68 degrees, and the number is 48; adopt the maximum elevation angle access scheme Access; 3. Under the statistical distribution model, considering the difference in user distribution density, the location and density difference of the source and target of the call, the channel occupancy of each inter-satellite link in the network is obtained. The 4th step further comprises sub-steps: one, according to the queuing theory, each inter-satellite link can be regarded as a single service window mixed system queuing model M/M/l/m, and each inter-satellite link only contains a single In the service window, the time interval between arrivals of "customers" obeys a negative exponential distribution with a parameter of β; the service time is a negative exponential distribution with a parameter of μ; each inter-satellite link has m queuing capacity. When there are already m data packets in the system, the new data packets will no longer enter the queue, and the data packets will be discarded. There is: ρ=β/μ; 2. The average waiting time delay of data packets is $W=\frac{1}{\mathrm{\&mu;}\&CenterDot;(1-\mathrm{\&rho;})}-\frac{m\&Center\; Dot;{\mathrm{\&rho;}}^m}{\mathrm{\&mu;}\&CenterDot;(1-{\mathrm{\&rho;}}^m)}.$ The routing algorithm in the sixth step is the FBellman-Ford routing algorithm.

According to a preferred embodiment of the present invention: the sixth step specifically includes sub-steps: six steps, the default service is the low-orbit layer in the multi-layer satellite network system, if the medium-orbit source satellite and the target satellite are the same, And the low-orbit source satellite and the target satellite are different, execute steps six and four; if the geostationary orbit source satellite and the target satellite are the same, and the low-orbit and medium-orbit source satellites and target satellites are different, execute steps six and five; otherwise, execute steps Step 62; Step 62: If the low-orbit layer path contains the number of inter-satellite links less than or equal to the low-orbit threshold of the inter-satellite link, perform step six and step three; if the low-orbit layer path contains the number of inter-satellite links Greater than the low-orbit threshold of the inter-satellite link, and the number of inter-satellite links contained in the mid-orbit layer path is less than or equal to the mid-orbit threshold of the inter-satellite link, perform steps 6 and 4; otherwise, perform steps 6 and 5; step 6 and 3: establish The optimal communication path at the low-orbit satellite layer to complete the transmission task; the sixth and fourth steps: establish the optimal communication path at the medium-orbit satellite layer to complete the transmission task; the sixth and fifth steps: establish the optimal communication path at the geostationary satellite layer to complete the transmission task; six Step six: Statistical parameters of the multi-layer network in the multi-layer satellite network system, and analyze network performance; Step six and seven: update the time interval, complete the calculation of the new routing table and complete the satellite handover. The Bellman-Ford routing algorithm that described step 63 steps, 64 steps and 65 steps are applied to, this algorithm comprises sub-steps: Step 1: make the T label value of all non-starting nodes in the network be ∞, namely T(i )=∞; Make the P label of the initial node be 0, that is, P(s)=0; Step 2: take the new P label as the initial node i, check whether each end point j of the edge with i as the initial node There is [P(i)+d(i, j)]<P(j) or [P(i)+d(i, j)]<T(j), if it exists, go to step 3, otherwise keep the original label ; Step 3: Change the T label or P label at point j to a new T label T(j)=P(i)+d(i, j) or T(i)+d(i, j). Take the minimum value of the existing T-labeled points in the network, set it as a new P-labeled point, and repeat Step 2; Step 4: When all nodes in the network are P-labeled points, the algorithm ends. The characteristic parameters that need to be counted in the six or six steps include: the memory usage percentage of each satellite node, the length of the inter-satellite link and the blocking probability.

Considering the orbits of polar orbits or near-polar orbits such as π-shaped constellations, there is a "gap" between the opposite-moving orbits, and the satellites on both sides of the gap cannot establish an inter-orbital link because of their relative motion; at the same time, the inter-orbital link is over the polar regions It must be closed, because adjacent satellite orbits cross over the polar regions, and the inter-satellite distance changes rapidly, so it is impossible to establish an ISL. The schematic diagram of the crossing relationship between adjacent orbits of the polar orbit constellation is shown. The relative position of the communication network satellite composed of Walker delta-2π inclined circular orbit constellation is fixed, and the ISL has a simple geometric structure and stable performance. The multi-layer satellite network can solve the problem of insufficient coverage in the high latitude areas of the Walker delta LEO constellation.

In addition, during the research process, it was found that the single-layer satellite network, especially the LEO and MEO satellite network, has a very close spatial distance between two satellites, but because there is no ISL direct connection, it cannot communicate directly, and must pass through several satellite paths established by ISL. Completing the communication will not only fail to meet the communication QoS, but also waste a lot of system and on-board resources, and even cause link congestion, as shown in the shortest path diagram between the low-orbit satellite 11 and the low-orbit satellite in the Walker delta constellation in Figure 3 Walker delta The shortest path between LEO satellite 11 and LEO satellite in the constellation.

The multi-layer satellite network with hierarchical structure can not only solve the above problems, but also integrate the advantages of the three single-layer satellites, give full play to its huge advantages in coverage, inter-satellite links, and delay requirements, and meet the requirements of various services. Require. A multi-layer satellite network is more effective than a single-layer network, with more flexible path selection, more replaceable links, and stronger survivability.

Fig. 4 is a schematic diagram of the coverage performance of a single-layer inclined circular orbit satellite constellation. The satellite constellation includes l circular orbits with an inclination angle of γ and a height of h, and there are m evenly distributed satellites on each orbit, the phase difference δ=2π/m, the right ascension difference of the ascending node of each orbit Ω=2π/l, The relative positions of satellites in adjacent orbits can be expressed by a and ω, and ΔM is the initial phase relative to the reference satellite 11 . The coverage of the Earth by a single satellite can be calculated using the following formula:

$\mathrm{<span\; class="notranslate">\; \&phi;</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; \&pi;</span>}<span\; class="notranslate">\; /</span>\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; \&epsiv;</span>}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; sin</span>}}^{<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; (</span>\frac{{\mathrm{<span\; class="notranslate">\; r</span>}}_{\mathrm{<span\; class="notranslate">\; E.</span>}}}{{\mathrm{<span\; class="notranslate">\; r</span>}}_{\mathrm{<span\; class="notranslate">\; E.</span>}}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; h</span>}}<span\; class="notranslate">\; \&CenterDot;</span>\mathrm{<span\; class="notranslate">\; cos</span>}\mathrm{<span\; class="notranslate">\; \&epsiv;</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; )</span>$

表示覆盖区域对应的地心角的一半。对于多层卫星网络，需要考虑上层卫星覆盖下层卫星的情况。可以按照式(2)来计算：In formula (1), ε represents the angle of belief in communication, r _E represents the radius of the earth, and the calculation result

Indicates half of the geocentric angle corresponding to the coverage area. For a multi-layer satellite network, it is necessary to consider the situation where the upper layer satellites cover the lower layer satellites. It can be calculated according to formula (2):

${\mathrm{\&phi;}}_i=\mathrm{\&pi;}/2-{\mathrm{\&epsiv;}}_i-{\sin }^{-1}(\frac{r_i}{r_i+h_i}\&Center\; Dot;\cos {\mathrm{\&epsiv;}}_i)$ i=1, 2, 3... (2)

Fig. 5 is the case of i=2 in expression (2) in the multi-layer satellite network system and routing setting method of the present invention, where ε ₂ =θ, r ₂ =r _L . r _L , r _M represent the orbit radius of LEO and MEO satellites, h ₁ represents the altitude of LEO satellite, h ₂ represents the difference between the orbit height of MEO and LEO satellite, s ¹ _L , s ² _L , s ⁿ _L and s ¹ _M , s ^N _M represents the satellite, d ₁ , d ₂ , and d ₃ represent the inter-satellite distance, θ represents the minimum elevation angle for communication between LEO and MEO, and the upper shadow in the figure represents the coverage of the MEO satellite to the LEO satellite layer, that is, the range where the ISL can be established. The shading below indicates the ground coverage of the LEO satellites. Calculating the inter-satellite distance only needs to bring the satellite coordinates into the formula (3):

$\mathrm{<span\; class="notranslate">\; d</span>}<span\; class="notranslate">\; =</span>\sqrt{{<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; x</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; x</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; )</span>}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; +</span>{<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; the\; <figure-callout\; id="1"\; label="y"\; filenames="A20081006614000212.png,A20081006614000241.png"\; state="\{\{state\}\}">y</figure-callout></span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; the\; y</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; )</span>}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; +</span>{<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; <figure-callout\; id="1"\; label="z"\; filenames="A20081006614000212.png,A20081006614000241.png"\; state="\{\{state\}\}">z</figure-callout></span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; z</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; )</span>}^{\mathrm{<span\; class="notranslate">\; 2</span>}}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 3</span>}<span\; class="notranslate">\; )</span>$

The coordinates (x, y, z) of the satellite in the earth’s fixed coordinate system can be calculated by formula (4):

$\left\{\begin{array}{c}\mathrm{<span\; class="notranslate">\; x</span>}<span\; class="notranslate">\; =</span><span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; r</span>}}_{\mathrm{<span\; class="notranslate">\; E.</span>}}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; h</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; \&Center\; Dot;</span><span\; class="notranslate">\; [</span>\mathrm{<span\; class="notranslate">\; cos</span>}\mathrm{<span\; class="notranslate">\; \&xi;</span>}<span\; class="notranslate">\; \&Center\; Dot;</span>\mathrm{<span\; class="notranslate">\; cos</span>}\mathrm{<span\; class="notranslate">\; \&rho;</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; sin</span>}\mathrm{<span\; class="notranslate">\; \&xi;</span>}<span\; class="notranslate">\; \&Center\; Dot;</span>\mathrm{<span\; class="notranslate">\; sin</span>}\mathrm{<span\; class="notranslate">\; \&rho;</span>}<span\; class="notranslate">\; \&Center\; Dot;</span>\mathrm{<span\; class="notranslate">\; cos</span>}\mathrm{<span\; class="notranslate">\; \&gamma;</span>}<span\; class="notranslate">\; ]</span>\\ \mathrm{<span\; class="notranslate">\; the\; y</span>}<span\; class="notranslate">\; =</span><span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; r</span>}}_{\mathrm{<span\; class="notranslate">\; E.</span>}}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; h</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; \&Center\; Dot;</span><span\; class="notranslate">\; [</span>\mathrm{<span\; class="notranslate">\; cos</span>}\mathrm{<span\; class="notranslate">\; \&xi;</span>}<span\; class="notranslate">\; \&Center\; Dot;</span>\mathrm{<span\; class="notranslate">\; sin</span>}\mathrm{<span\; class="notranslate">\; \&rho;</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; sin</span>}\mathrm{<span\; class="notranslate">\; \&xi;</span>}<span\; class="notranslate">\; \&Center\; Dot;</span>\mathrm{<span\; class="notranslate">\; cos</span>}\mathrm{<span\; class="notranslate">\; \&rho;</span>}<span\; class="notranslate">\; \&Center\; Dot;</span>\mathrm{<span\; class="notranslate">\; cos</span>}\mathrm{<span\; class="notranslate">\; \&gamma;</span>}<span\; class="notranslate">\; ]</span>\\ \mathrm{<span\; class="notranslate">\; z</span>}<span\; class="notranslate">\; =</span><span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; r</span>}}_{\mathrm{<span\; class="notranslate">\; E.</span>}}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; h</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; \&Center\; Dot;</span>\mathrm{<span\; class="notranslate">\; sin</span>}\mathrm{<span\; class="notranslate">\; \&xi;</span>}<span\; class="notranslate">\; \&Center\; Dot;</span>\mathrm{<span\; class="notranslate">\; sin</span>}\mathrm{<span\; class="notranslate">\; \&gamma;</span>}\end{array}\right.<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 4</span>}<span\; class="notranslate">\; )</span>$

In formula (4)

ξ＝ω ₀ +v ₀ +v·(tt ₀ ) (5)

ρ=ζ-v _E ·(tt ₀ ) (6)

ω ₀ is the argument of perigee, v ₀ is the initial true anomaly angle of the satellite, and v is the angular velocity of the satellite motion, where $v=\sqrt{\mathrm{\&mu;}/{\mathrm{<figure-callout\; id="3"\; label="r"\; filenames="A20081006614000212.png,A20081006614000242.png"\; state="\{\{state\}\}">r</figure-callout>}}^3},$ μ is the gravitational constant of the earth, r is the orbital radius of the satellite, tt ₀ is the running time of the satellite, t ₀ is the initial moment, ξ is the true anomaly, ζ is the right ascension of the ascending node, and v _E is the angular velocity of the earth.

Table 1:

satellite layer GEO MEO LEO Number of satellites (pieces) 3 12 48 Orbit height (km) 35786 10355 1400 Orbital inclination (degrees) 0.0 55.0 52.0 orbital period 24 hours 6 hours 114 minutes number of tracks 1 3 8 Constellation type synchronous orbit Walker delta constellation Walker delta constellation Layer-to-layer link (piece/piece) GEO->MEO 4 MEO-＞GEO 1MEO-＞LEO 4 LEO->MEO 1 Links of the same layer (piece/piece) 2 2 within the track + 2 between the tracks 2 within the track + 2 between the tracks Inter-layer link status non-permanent Non-permanent non-permanent Peer link status permanent permanent permanent Tong Faith Angle (degrees) 20 twenty two 10 Coverage ±61.8° range Global coverage ±68.1° range

If one GEO satellite is used for regional coverage, it can be selected according to needs, such as covering the surrounding areas of China (east longitude 67.5° to 172.5°, north and south latitude 54° range, including Central Asia, East Asia and Oceania, etc.), the satellite is located at east longitude 120.0 ° above. If it covers the whole world, for example, the three GEO satellites in the multi-layer satellite network proposed in this paper are located at 0.0°, 120.0° and 240.0° east longitude. Table 1 gives the structural parameters of the multi-layer satellite network, and the spatial structure diagram of MLSN is shown in Fig. 6, the schematic diagram of the mathematical model for calculating the satellite inter-satellite link.

Each MEO satellite has four permanent ISLs in the MEO layer, the geometric parameters of the ISLs in the two orbits are fixed, and the geometric parameters of the permanent ISLs between the two orbits are time-varying. The ISL conditions of other MEO satellites are similar to those of MEO satellite 11, but the initial phases are different. A total of 24 ISLs are contained in the MEO satellite layer. Also each LEO satellite has 4 permanent ISLs within the layer, two intra-orbital and two inter-orbital. A total of 96 ISLs are contained in the LEO satellite layer.

For the interlayer link, although each LEO satellite can see multiple MEO and GEO satellites at the same time, in order to simplify the structure and consider the actual communication needs, each LEO satellite selects one MEO satellite, and each MEO satellite only has one GEO satellite Create a link. The calculation results of geometric parameters of ISLs between LEO/MEO satellite orbits are shown in Table 2, taking satellite 11 as an example.

The mathematical model for calculating the satellite ISL is shown in Figure 7. The schematic diagram of the mathematical model for calculating the satellite inter-satellite link is shown. The relationship between the average delay and ISL in the multi-layer satellite network is shown in Figure 8. The average delay and the number of inter-satellite links in the multi-layer satellite network The schematic diagram of the relationship is shown. The average delay is almost linear with the number of ISLs on the path. It can be seen that GEO satellites are not suitable for transmitting voice services, because the voice service requires a delay of less than 200ms, and if the MEO network transmits voice services, the delay requires at most one ISL on the path. Of course, if the path contains more than 6 ISLs in the LEO network, the average delay is also greater than 200ms. Both LEO and MEO networks can meet the 400ms transmission delay recommended by CCITT.

Table 2

The routing calculation adopts the Bellman-Ford backward algorithm, and the judgment of the optimal path is the comprehensive weight of the path (TPW: Total path weight). TPW represents the comprehensive performance of a path's delay and bandwidth occupation, and it is also effective and reliable. Comprehensive performance. TPW consists of three parts, the uplink delay D _u , the downlink delay D _d and the link weight of each ISLw _i on the path Indicates the set of ISLs on the path W={w ₁ , w ₂ ...w _i ...w _ns-1 }, |W|=n _s -1 means that the path contains n _s -1 ISLs, n _s is the number of satellites on the path (including source satellites and target satellites). After the ground source and target positions are determined, the source satellite and target satellite are selected using the maximum elevation angle access scheme to form an end-to-end link.

$\mathrm{<span\; class="notranslate">\; TPW</span>}<span\; class="notranslate">\; =</span>\underset{{\mathrm{<span\; class="notranslate">\; w</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}<span\; class="notranslate">\; \&Element;</span>\mathrm{<span\; class="notranslate">\; W</span>}}{\mathrm{<span\; class="notranslate">\; \&Sigma;</span>}}{\mathrm{<span\; class="notranslate">\; LW</span>}}_{{\mathrm{<span\; class="notranslate">\; w</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; D.</span>}}_{\mathrm{<span\; class="notranslate">\; u</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; D.</span>}}_{\mathrm{<span\; class="notranslate">\; d</span>}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 7</span>}<span\; class="notranslate">\; )</span>$

in

${\mathrm{<span\; class="notranslate">\; LW</span>}}_{{\mathrm{<span\; class="notranslate">\; w</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; D.</span>}}_{{\mathrm{<span\; class="notranslate">\; w</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; f</span>}<span\; class="notranslate">\; \&Center\; Dot;</span>{\mathrm{<span\; class="notranslate">\; W</span>}}_{{\mathrm{<span\; class="notranslate">\; w</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 8</span>}<span\; class="notranslate">\; )</span>$

表示

的传输时延，

表示平均等待时延，f是信息量权重参数。D_u、D_d和

的求解只需知道卫星空间位置坐标，用链路长度除以传输速度即可，无需冗述。

express

the transmission delay,

Indicates the average waiting delay, and f is the weight parameter of the amount of information. D _u , D _d and

To solve it, we only need to know the coordinates of the satellite space position, and divide the link length by the transmission speed, so there is no need to elaborate.

According to the Jackson principle, each ISL can be regarded as a single service window mixed queuing model M/M/l/m, and the interval between arrivals of data packets obeys a negative exponential distribution, and the parameter is β; the service time is a parameter whose μ is a negative exponent Distribution; each ISL has m queuing capacity. When there are m data packets in the system, the new incoming data packets will be transferred to other satellites for processing.

have

ρ=β/μ (9)

The average waiting time of packets is

$\mathrm{<span\; class="notranslate">\; W</span>}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; \&mu;</span>}<span\; class="notranslate">\; \&CenterDot;</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; \&rho;</span>}<span\; class="notranslate">\; )</span>}<span\; class="notranslate">\; -</span>\frac{\mathrm{<span\; class="notranslate">\; m</span>}<span\; class="notranslate">\; \&CenterDot;</span>{\mathrm{<span\; class="notranslate">\; \&rho;</span>}}^{\mathrm{<span\; class="notranslate">\; m</span>}}}{\mathrm{<span\; class="notranslate">\; \&mu;</span>}<span\; class="notranslate">\; \&Center\; Dot;</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; \&rho;</span>}}^{\mathrm{<span\; class="notranslate">\; m</span>}}<span\; class="notranslate">\; )</span>}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 10</span>}<span\; class="notranslate">\; )</span>$

The multi-layer satellite network adaptive IP routing strategy has the following characteristics: services are connected to the satellite system through LEO source satellites and target satellites, and the satellite layer for transmitting the services is selected according to the QoS requirements and network status. If the network resources of the LEO layer cannot meet the service requirements , transfer the service to MEO layer transmission, or even GEO layer transmission. For the situation where the ground source/target is directly connected to MEO or GEO satellites, because the routing algorithm is simple to implement, it is not analyzed in detail. In addition, according to the schematic diagram and simulation results of the relationship between the average delay and the number of inter-satellite links in the multi-layer satellite network in Figure 8, if the path of the LEO layer contains 6 or 7 ISLs, the delay will be greater than 200ms. The business is transferred to MEO, the transmission time is shorter, and the on-board resources are occupied less. Moreover, if the ground source and the target position are covered by the same MEO or GEO satellite, this service is transferred to MEO and GEO transmission to reduce the occupancy of on-board resources. The strategy considers the delay index and ISL bandwidth occupation status, and the optimal path selection takes into account the effectiveness and reliability of the satellite system. Other parameters required in the calculation process of the algorithm are set as shown in Table 3. Table 4 shows the call percentage between call source and target area.

table 3

parameters value

ISL channel capacity (Kbps) 400～10,000 Total network traffic (packets/s) 2000～100,000 Average packet length (bytes) 200～20,000 Packet length mean square error value (bytes) 30～3,000 Simulation time (min) 114/360 Information weight parameter f {0, 1, 10, 100} ISL buffer (packets) 25 ISL_LEO Threshold 5 ISL_MEO Threshold 2

Table 4

The multi-layer structure effectively shares the network load, and can reduce TPW when other relevant parameters are the same, as shown in Figure 9. Compared with LEO network or MEO network, the path TPW of MLSN is smaller than that of single-layer satellite network. The multi-layer satellite network composed of the Walker delta constellation has permanent ISL, which can ensure the effectiveness of the satellite network, and has higher reliability than the single-layer satellite network. In the case of damage to satellite nodes or communication links, more The alternative path will not cause a significant drop in service performance. The adaptive IP routing strategy under the statistical distribution business model considers the information load changes of all ISLs in the network, and adaptively selects the optimal path. The multi-layer satellite network can meet the different service quality requirements of various businesses, especially without increasing the transmission delay and delay jitter, obtain a smaller comprehensive path weight, reduce the probability of packet loss, and is suitable for forming service quality requirements A variety of business comprehensive networks with large differences and military satellite communication networks with different priorities.

Compared with traditional geostationary orbit satellites, the technology described in the present invention consists of low-orbit and middle-orbit satellites to form a global coverage network, with small transmission delay and high effectiveness. Satellites have on-board processing and switching capabilities, and inter-satellite microwave or optical links can provide broadband integrated services to users around the world, effectively guaranteeing service quality, and the path selection is more flexible, and there are many replaceable links. The anti-destroy performance is stronger.

The above content is a further detailed description of the present invention in conjunction with specific preferred embodiments, and it cannot be assumed that the specific implementation of the present invention is limited to these descriptions. For those of ordinary skill in the technical field of the present invention, without departing from the concept of the present invention, some deduction or replacement can be made, which should be regarded as belonging to the protection scope of the present invention.

Claims (8)

1. A multi-layer satellite network system routing setting method is characterized in that: the routing setting method comprises steps: A: Set parameters and perform network initialization; B: Fix a time t _k , in this time interval Δt, solve the satellite orbit parameters, calculate the satellite position coordinates and the length of the inter-satellite link, and establish the network topology; C: Calculate the inter-satellite link load of the multi-layer satellite network according to the set business model; D: Calculate the delay of on-board processing and switching according to the queuing theory; E: Find the source satellite and target satellite in each satellite layer according to the position of the ground source target; F: Select the satellite layer of the transmission service according to the communication service instruction requirements and the network status, and find the optimal path according to the routing algorithm. 2. according to the described multi-layer satellite network system route setting method of claim 1, it is characterized in that: the parameter setting in the described step A comprises: multi-layer satellite network layer number, satellite number in each layer, inter-satellite link Number of satellites, orbit type of each satellite, orbit height, orbit inclination and number of orbits. 3. according to the described multi-layer satellite network system route setting method of claim 1, it is characterized in that: described step C further comprises sub-step: C1: Under the non-uniform distribution model, the population density is divided into 5 levels, and the population density in each area is represented by numbers; C2: Divide the earth's surface into 48 parts, adopt the method of dividing parallel to the latitude and inclined to the longitude, and the 8 oblique lines form 52 degrees with the latitude, divide the longitude 360 degrees into 8 parts, and the latitude into 6 parts; There is one ground station in the area, and the ground stations are located at 15 degrees, 45 degrees and 68 degrees north and south latitude, and the number is 48; the access scheme with the largest elevation angle is used for access; C3: Under the statistical distribution model, consider the difference in user distribution density, the location and density difference of the source and target of the call, and obtain the channel occupancy of each inter-satellite link in the network. 4. according to the said multi-layer satellite network system routing setting method of claim 1, it is characterized in that: said step D further comprises sub-steps: D1: According to the queuing theory, each inter-satellite link is regarded as a single service window mixed queuing model M/Ml/m, each inter-satellite link only contains a single service window, and the interval between the arrival of "customers" obeys a negative index distribution, the parameter is β; the service time is a negative exponential distribution with the parameter μ; each inter-satellite link has m queuing capacity, when there are m data packets in the system, the new data packets will no longer enter the queue, There is: ρ=β/μ; D2: The average waiting delay of data packets is $W=\frac{1}{\mathrm{\&mu;}\&CenterDot;(1-\mathrm{\&rho;})}-\frac{m\&Center\; Dot;{\mathrm{\&rho;}}^m}{\mathrm{\&mu;}\&Center\; Dot;(1-{\mathrm{\&rho;}}^m)}.$ 5. The multi-layer satellite network system routing setting method according to claim 1, characterized in that: the routing algorithm in the step F is the FBellman-Ford routing algorithm. 6. according to claim 1 or 5 described multi-layer satellite network system route setting method, it is characterized in that: described step F specifically comprises sub-step: F1: The default service in the multi-layer satellite network system is the low-orbit layer. If the medium-orbit source satellite and target satellite are the same, and the low-orbit source satellite and target satellite are different, perform step F4; if the geostationary orbit source satellite and target If the satellites are the same, and the low-orbit and medium-orbit source satellites and target satellites are different, go to step F5; otherwise, go to step F2; F2: If the number of inter-satellite links included in the low-orbit layer path is less than or equal to the low-orbit threshold of inter-satellite links, perform step F3; if the number of inter-satellite links contained in the low-orbit layer path is greater than the low-orbit threshold of inter-satellite links , and the number of inter-satellite links included in the mid-orbit path is less than or equal to the inter-satellite link mid-orbit threshold, execute step F4; otherwise, execute step F5; F3: Establish the optimal communication path at the low-orbit satellite layer and complete the transmission task; F4: Establish the optimal communication path at the mid-orbit satellite layer and complete the transmission task; F5: Establish the optimal communication path at the geostationary satellite layer and complete the transmission task; F6: counting the characteristic parameters of the multi-layer network in the multi-layer satellite network system, and analyzing the network performance; F7: Update the time interval, complete the calculation of the new routing table and complete the satellite handover. 7. according to claim 6 described multi-layer satellite network system routing setting method, it is characterized in that: the described Bellman-Ford routing algorithm that described step F3, F4 and F5 are applied to, this algorithm comprises substep: Step 1: Let the T label value of all non-initial nodes in the network be ∞, that is, T(i)=∞; make the P label of the initial node be 0, that is, P(s)=0; Step 2: With the new P label as the starting node i, check whether there is [P(i)+d(i, j)]<P(j) or [ P(i)+d(i, j)]<T(j), if it exists, go to step 3, otherwise keep the original label; Step 3: Change the T label or P label at point j to a new T label T(j)=P(i)+d(i,j) or T(i)+d(i,j). Get the minimum value of the existing T label points in the network, set it as a new P label point, and repeat step 2; Step 4: When all nodes in the network are P-labeled points, the algorithm ends. 8. according to claim 6 said multi-layer satellite network system route setting method, it is characterized in that: the characteristic parameter that needs to carry out statistics in the described step F6 comprises: the memory occupation percentage of each satellite node, inter-satellite link length and blocking probability.

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