CN113507314B - Inter-satellite data transmission method - Google Patents
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- CN113507314B CN113507314B CN202110951571.3A CN202110951571A CN113507314B CN 113507314 B CN113507314 B CN 113507314B CN 202110951571 A CN202110951571 A CN 202110951571A CN 113507314 B CN113507314 B CN 113507314B
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04B—TRANSMISSION
- H04B7/00—Radio transmission systems, i.e. using radiation field
- H04B7/14—Relay systems
- H04B7/15—Active relay systems
- H04B7/185—Space-based or airborne stations; Stations for satellite systems
- H04B7/1851—Systems using a satellite or space-based relay
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04B—TRANSMISSION
- H04B7/00—Radio transmission systems, i.e. using radiation field
- H04B7/14—Relay systems
- H04B7/15—Active relay systems
- H04B7/185—Space-based or airborne stations; Stations for satellite systems
- H04B7/18521—Systems of inter linked satellites, i.e. inter satellite service
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
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- Y02D—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN INFORMATION AND COMMUNICATION TECHNOLOGIES [ICT], I.E. INFORMATION AND COMMUNICATION TECHNOLOGIES AIMING AT THE REDUCTION OF THEIR OWN ENERGY USE
- Y02D30/00—Reducing energy consumption in communication networks
- Y02D30/70—Reducing energy consumption in communication networks in wireless communication networks
Abstract
The invention provides an inter-satellite data transmission method, which comprises the following steps: the inter-satellite link is utilized to assist in unloading feed data, and the satellite transmits data to be unloaded to a ground satellite with residual bandwidth through the inter-satellite link so as to utilize feed bandwidth resources; the iterative algorithm CDD is developed based on MFMC linear programming constrained by the tape map to maximize system throughput and minimize data transmission delay.
Description
Technical Field
The invention relates to the technical field of LEO satellites, in particular to an inter-satellite data transmission method.
Background
In recent years, broadband LEO satellite networks have attracted considerable academic and industrial attention. An important task of satellite constellations is to forward user data stores to gateway stations as spatial routers. However, unlike inter-satellite link (ISLs) resources, which are rich in space segments, the feeder link resources established by satellites and gateway stations are limited, which becomes a bottleneck for the capacity of the entire LEO satellite network. And thus fully utilizing feeder link resources is critical to improving overall network throughput.
Disclosure of Invention
The invention aims to provide an inter-satellite data transmission method to solve the problem that the feed link resources established by the existing satellites and gateway stations are limited and become the bottleneck of the whole LEO satellite network capacity.
In order to solve the above technical problems, the present invention provides an inter-satellite data transmission method, including:
the inter-satellite link is utilized to assist in unloading feed data, and the satellite transmits data to be unloaded to a ground satellite with residual bandwidth through the inter-satellite link so as to utilize feed bandwidth resources;
the iterative algorithm CDD is developed based on MFMC linear programming constrained by the tape map to maximize system throughput and minimize data transmission delay.
Optionally, in the inter-satellite data transmission method, the method further includes:
the satellite network consists of N orbits, and each orbit comprises M satellites;
the LEO satellite network is represented by graph g= (V, E), where V represents a set of nodes and E represents a set of ISLs links, including inter-satellite links and feeder links;
ISLs are established through a laser terminal on a satellite and a neighbor satellite;
by l i,j Representing satellite v i And v j Inter-satellite link with inter-satellite communication via laser terminals, and l i,j ∈E；
The ISLs in the tracks are kept all the time, the ISLs between the tracks in the polar region are temporarily disconnected, and the chain is rebuilt after leaving the polar region;
two satellites on adjacent orbits pass through the polar region and then exchange relative positions to form a twisted Manhattan network, and the upper half part of the twisted Manhattan network is rotated by 180 degrees;
the polar orbit LEO satellite network has a fixed two-dimensional Mash structure, and the dynamic property of the LEO satellite network is determined by the fact that ISLs between orbits are switched on and switched off due to polar regions and the error rate of a laser terminal is too high to build a chain due to sunlight interference.
Optionally, in the inter-satellite data transmission method, the method further includes:
V ES e, V represents a set of ground satellites connected with the gateway station through a feed link;
floor satellite v i Establishing a feed link W with a gateway station i ；
Each satellite has 16 spot beams with fixed directions for communication with users, and a feed link is established through an antenna and a gateway station ES;
a plurality of gateway stations are distributed globally, each gateway station is provided with k antennas, and feed links are established with k satellites at the same time;
the satellite downloads data to the gateway station in the sight range of the gateway station ES, which is called a downloading time window; the satellite operating period is divided into time slots of equal length τ, with the time lines indicated as 0,1 τ,2 τ.
Optionally, in the inter-satellite data transmission method, the method further includes:
for any link l n Total capacity C n Represented as
Wherein eta n ,
β n And W is n Respectively representing the frequency spectrum efficiency, the multipath gain, the frequency multiplexing coefficient and the bandwidth allocated by the link;
calculating satellite v i Total capacity of feed link B i ；
The instantaneous transmission rate of data is denoted as r n ＝ρ n x n Wherein ρ, x n Instantaneous traffic (packets/sec) for the packet size and link, respectively;
in satellite v i In the absence of congestion or failure of all inter-satellite links, i.e
Data transfer rate offloaded over feeder link is
When l i -B i >0, representing satellite v i Failure to offload all data to gateway station, packet loss occurs, otherwise satellite v is indicated i The feed link has a margin in bandwidth, at which time the feed link data transmission rate b i ＝l i The method comprises the steps of carrying out a first treatment on the surface of the Make full use of the feed resources
maxΣ i |l i -B i | (3)
Optionally, in the inter-satellite data transmission method, the method further includes:
transmitting data packets with the same size between all satellites and between the satellites and the gateway station;
the amount of data that the satellite needs to transmit to the gateway station is expressed as the number of data packets, the number of data packets being expressed in terms of link rate;
each satellite is provided with 4 laser terminals to establish inter-satellite links with adjacent 4 satellites in the same orbit and different orbits, and simultaneously is provided with a wireless signal transmitting and receiving terminal and a gateway station to establish feed links, and the links work in a simplex mode;
the data transmission of the inter-satellite link and the feeder link is error-free;
firstly, determining and obtaining the traffic transmission requirement, including the source and destination of the data to be unloaded to the gateway station and the data transmission rate through ISLs, and then calculating the forwarding path of the data packet between the ground satellites according to the requirement.
Optionally, in the inter-satellite data transmission method, the method further includes:
let the
Representing real set, traffic demand matrix->
The element D (i, j) represents the data transmission rate required between a pair of satellites, and then the maximum flow minimum cost algorithm is used to calculate the link traffic matrix +_based on the matrix>
Wherein each element R (i, j) represents the data transmission rate after each inter-satellite link route;
when each time slot nτ starts, updating parameters such as a network topological structure, link capacity of each satellite inter-satellite link and feed link, instantaneous transmission rate and the like;
when in the above formula I i -B i <0, i.e. satellite v i Capable of additionally receiving an offloaded data stream l I Such satellite sets are V I The method comprises the steps of carrying out a first treatment on the surface of the And according to the inter-satellite link and feeder link capacity of the satellite, calculating a receivable data stream by the following formula;
when in the above formula I i -B i >0, i.e. satellite v i Data stream l may need to be offloaded via ISLs O Such satellite sets are V O According to the inter-satellite link resource capacity of the satellite, calculating the data flow to be unloaded according to the following formula;
according to satellite set V O And V I Each satellite l O And l I The magnitude of the value, the two satellites are concentrated in a one-to-one correspondence according to the order of the value from large to small, the two satellites are respectively used as the source and the destination of data transmission, and the min (l O ,l I ) As the source-to-destination demand traffic rate D (i, j); thereby obtaining a traffic demand matrix D.
Optionally, in the inter-satellite data transmission method, the method further includes:
at the cost of the link distance bandwidth product (BD), allowing shorter paths to be planned for larger traffic, minimizing transmission costs and preventing loop-backs;
sub-graph constraint is carried out on the data flow in each pair of sources and destinations according to energy and computing resources, namely linear programming of the data flow can only be carried out in a corresponding sub-graph, so that the operation complexity is reduced.
Optionally, in the inter-satellite data transmission method, the method further includes:
in the satellite network topology graph G (V, E), the obtained traffic demand matrix is used for generating a traffic demand matrix
Computing subgraph G with distance constraints c (V c ,E c )∈G(V,E)；
Calculating shortest paths from all nodes in a ground satellite area to other nodes in the area by using a Dijkstra shortest path algorithm, initializing a group of candidate nodes and candidate edge sets into NULL by using data flows in a source/destination pair (s, d);
traversing other intermediate nodes in the area, using M (s, d) to represent the hop count of the (s, d) shortest path, and taking a proper hop count threshold HT;
if the intermediate node V meets M (s, V) +M (V, d) +M (s, d) +HT, adding the node V and four inter-star links thereof into the node set V of the subgraph c Sum edge set E c In (a) and (b);
computing subgraph G for each data stream c And then, carrying out linear programming on the maximum flow minimum cost routing algorithm.
Optionally, in the inter-satellite data transmission method, the method further includes:
by performing distance constraint on the data streams of each pair of sources/sinks (s, d), a corresponding sub-graph is obtained, and the maximum data stream linear programming problem of multiple sources and multiple sinks under the limitation of the sub-graph is represented as formula (7):
Subject to:
wherein l c (e) Representing the flow rate on edge e;
and b c (v) Respectively representing the total flow rate of the node v flowing in and out through the inter-satellite links and the feed link flow rate; d (D) c Representing corresponding request flow in the flow demand matrix; in the formula (7), the constraint on the link capacity is shown as (7.1) - (7.3); (7.4) - (7.6) are constraints on the traffic balance in the network for each sub-graph; (7.7) constraining each data stream to a rate not exceeding the demand; the maximum flow from multiple sources to multiple purposes in the network can be obtained by solving the linear programming; />
To obtain the minimum achievable routing cost, a second linear programming problem is as in equation (8);
min:y * (8)
Subject to:
wherein Γ is c Representing the maximum flow rate of the flow c obtained by solving the maximum flow linear programming problem, V' =v-(s) c ,d c )；
The (8.1) in the formula (8) requires the fixed speed of each flow, and is obtained by the formula (7); the remaining constraints are similar to the previous LP constraints;
the objective function is to have all the data flow rates on each side
The sum of the products of the link cost M (e) is minimum;
and solving the two linear programming problems by adopting a greedy algorithm to obtain the maximum flow minimum cost route in the network.
Optionally, in the inter-satellite data transmission method, the method further includes:
after more than one round of calculation is completed, updating and iterating the network topology, and accelerating the convergence speed for reducing iteration rounds, if V I Satellite in collection I <Alpha, the satellite exits set V I The method comprises the steps of carrying out a first treatment on the surface of the If V O Satellite in collection O =0, then the set V is also exited O The method comprises the steps of carrying out a first treatment on the surface of the Residual V I And V O The middle node repeats the calculation process until V O Or V I The number of the middle nodes is 0, and all data flows can be smoothThe full throughput of the transmission to the gateway station or the feeding resource reaches the maximum, and the iterative process is ended until the next time slot tau starts the next round of operation.
The inventor of the present invention has found through research that, with the wide application of the internet and the rapid development of space-related technologies, a LEO (Low Earth Orbit) satellite network has become an important component of a mobile communication network. In recent years, the application of satellite laser communication terminals enables inter-satellite links to have higher bandwidths, and the bandwidth of resources on the satellites becomes richer. However, after the user data is forwarded by the space router carried by the satellite, the user data needs to be transmitted to the ground core network through the gateway stations, the visible landing number of each gateway station is limited, the gateway stations and the feed links of the landing satellites still depend on wireless transmitting and receiving ends, the link bandwidth is low, attenuation is caused by the influence of the distance, angle, cloud layer thickness and the like of the satellite and the gateway stations, and the feed link resources of the landing satellites and the gateway stations are deficient, so that the feed links established by the landing satellites and the gateway stations are very easy to become the capacity bottleneck of the whole broadband LEO satellite network.
The inventor of the present invention also found that, due to the low and different bandwidths of the feeder links, when a data packet is transmitted downstream from the satellite to the gateway station, a situation occurs in which a certain link bandwidth is occupied and other link bandwidths have a large margin, so that the precious feeder link bandwidth cannot be fully utilized.
Aiming at the problems, in order to fully utilize bandwidth resources of a feed link and reduce queuing delay in the process of downloading data packets from a ground satellite to a gateway station, the invention provides a routing algorithm aiming at the data packets to be downloaded from the ground satellite to the gateway station, which utilizes inter-satellite laser links between the ground satellites to perform data scheduling and assist data downlink transmission and avoids the increase of data packet delay or packet loss caused by accumulation of a large amount of data on the feed link with insufficient bandwidth.
In addition, low-orbit satellite networks have received much attention in recent years because of their lower latency and higher bandwidth. But the dynamics and periodicity of the low orbit satellite network present new challenges to the design of the routing protocol. The inventor of the present invention has found through research that, in the prior art, the bottleneck of the current low-orbit satellite network capacity is not considered as a feeder link, and the routing strategy of the space segment cannot effectively improve the throughput of the whole network. In addition, the prior art mainly focuses on data unloading of remote sensing observation types, the production and arrival of data packets in a broadband low-orbit satellite have randomness, the network traffic mode is more complex, and the requirement on end-to-end time delay is higher. The above work cannot accommodate these features.
Based on the above insight, the inventors come to the following conclusion: how to utilize the inter-satellite links between the ground satellites to facilitate the real-time download of data to gateway stations is a very challenging problem. The main difficulties are as follows: (1) The feeder link bandwidth of each drop point satellite is inconsistent with the amount of data that needs to be downloaded. Some ground satellites have large data volume, but bandwidth is reduced due to attenuation caused by weather, link angles and other problems, but on the contrary, some satellites with sufficient bandwidth have small data volume to be downloaded, so that the data flow between the ground satellites is planned by a design algorithm for fully utilizing the feed bandwidth, and the source, sink and transmission path of data transmission are determined. (2) Because a large amount of data is concentrated in the ground satellite area, the inter-satellite link resources of the ground satellite are also very tight, and the factors such as the residual bandwidth, the link quality and the like of the inter-satellite link must be comprehensively considered when the design algorithm performs inter-ground satellite data stream transmission. (3) Because of limited on-board computing resources, high requirements are placed on the complexity and instantaneity of the algorithm. In order to cope with these difficulties, the collaborative date downloading algorithm (Collaborative Date Downloading, abbreviated as CDD algorithm) provided by the invention calculates a routing table according to the residual feed bandwidth of the ground satellite, forwards the data packet to be downloaded from the ground satellite with insufficient residual feed bandwidth to other satellites with sufficient bandwidth, and then transmits the data packet from the satellite to the gateway station, so that the data packet can be more quickly transmitted to the gateway station through the feed link with higher bandwidth, and the network throughput is improved. And in consideration of the shortage of calculation and storage resources on the satellite, a hop count constraint is put forward on the algorithm to reduce the calculation complexity.
In the inter-satellite data transmission method provided by the invention, a scheme for assisting in unloading feed data by using inter-satellite links is provided, and feed bandwidth resources are fully utilized by allowing satellites to send data to be unloaded to the ground satellite with residual bandwidth through ISLs. The invention also provides a MFMC linear programming problem with graph constraint, and develops an iterative algorithm CDD to maximize system throughput and minimize data transmission delay. Simulation work was performed by Systems Tool Kit (STK) and simulation results showed that the proposed algorithm IACD was superior to the conventional Genetic algorithm in terms of throughput and latency. The invention focuses on data transmission between ground satellites.
The invention provides a cooperation scheme between feed links, and data packets which cannot be smoothly downloaded are routed to a proper satellite according to the bandwidth allowance of the satellite feed links and the inter-satellite links and then are downloaded to a gateway station, so that the data unloading throughput is improved to the maximum extent. Considering limited computational resources on satellites, an iterative MFMC routing algorithm with hop constraints is provided to solve the problems of inter-satellite data transmission and data downloading, the algorithm solves the problems through two Linear Programming (LP), and the two LPs can be solved in polynomial time.
Drawings
FIG. 1 is a schematic diagram of an inter-satellite data transmission method polar orbit LEO satellite network system according to an embodiment of the present invention;
FIG. 2 is a schematic diagram of a system model of an inter-satellite data transmission method according to an embodiment of the invention;
FIG. 3 is a schematic diagram of data flow of an inter-satellite link and feeder link of a satellite node according to an embodiment of the present invention;
FIG. 4 is a schematic diagram of a multi-hop routing in an LEO satellite network according to an inter-satellite data transmission method according to an embodiment of the present invention;
FIG. 5 is a schematic diagram illustrating an iteration of a method for inter-satellite data transmission according to an embodiment of the present invention;
FIG. 6 is a schematic diagram of an inter-satellite data transmission method according to an embodiment of the invention;
FIG. 7 is a schematic diagram of throughput of different data loads of an inter-satellite data transmission method according to an embodiment of the present invention;
FIG. 8 is a schematic diagram illustrating the end-to-end delay of different data loads in an inter-satellite data transmission method according to an embodiment of the present invention;
FIG. 9 is a schematic diagram illustrating a ratio of end-to-end delay of 40% data load in an inter-satellite data transmission method according to an embodiment of the invention;
fig. 10 is a schematic diagram of an end-to-end delay ratio of 120% data load in an inter-satellite data transmission method according to an embodiment of the invention.
Detailed Description
The invention is further elucidated below in connection with the embodiments with reference to the drawings.
It should be noted that the components in the figures may be shown exaggerated for illustrative purposes and are not necessarily to scale. In the drawings, identical or functionally identical components are provided with the same reference numerals.
In the present invention, unless specifically indicated otherwise, "disposed on …", "disposed over …" and "disposed over …" do not preclude the presence of an intermediate therebetween. Furthermore, "disposed on or above" … merely indicates the relative positional relationship between the two components, but may also be converted to "disposed under or below" …, and vice versa, under certain circumstances, such as after reversing the product direction.
In the present invention, the embodiments are merely intended to illustrate the scheme of the present invention, and should not be construed as limiting.
In the present invention, the adjectives "a" and "an" do not exclude a scenario of a plurality of elements, unless specifically indicated.
It should also be noted herein that in embodiments of the present invention, only a portion of the components or assemblies may be shown for clarity and simplicity, but those of ordinary skill in the art will appreciate that the components or assemblies may be added as needed for a particular scenario under the teachings of the present invention. In addition, features of different embodiments of the invention may be combined with each other, unless otherwise specified. For example, a feature of the second embodiment may be substituted for a corresponding feature of the first embodiment, or may have the same or similar function, and the resulting embodiment would fall within the disclosure or scope of the disclosure.
It should also be noted herein that, within the scope of the present invention, the terms "identical", "equal" and the like do not mean that the two values are absolutely equal, but rather allow for some reasonable error, that is, the terms also encompass "substantially identical", "substantially equal". By analogy, in the present invention, the term "perpendicular", "parallel" and the like in the table direction also covers the meaning of "substantially perpendicular", "substantially parallel".
The numbers of the steps of the respective methods of the present invention are not limited to the order of execution of the steps of the methods. The method steps may be performed in a different order unless otherwise indicated.
The inter-satellite data transmission method provided by the invention is further described in detail below with reference to the accompanying drawings and specific embodiments. Advantages and features of the invention will become more apparent from the following description and from the claims. It should be noted that the drawings are in a very simplified form and are all to a non-precise scale, merely for convenience and clarity in aiding in the description of embodiments of the invention.
The invention aims to provide an inter-satellite data transmission method to solve the problem that the feed link resources established by the existing satellites and gateway stations are limited and become the bottleneck of the whole LEO satellite network capacity.
In order to achieve the above object, the present invention provides an inter-satellite data transmission method, including: the inter-satellite link is utilized to assist in unloading feed data, and the satellite transmits data to be unloaded to a ground satellite with residual bandwidth through the inter-satellite link so as to utilize feed bandwidth resources; the iterative algorithm CDD is developed based on MFMC linear programming constrained by the tape map to maximize system throughput and minimize data transmission delay.
The present invention mainly researches the polar orbit constellation (or Walker constellation) using ISLs as shown in FIG. 1. The satellite network consists of N orbits, each containing M satellites. The LEO satellite network is represented by the graph g= (V, E), where V represents the set of nodes and E represents the set of ISLs links, including inter-satellite links and feeder links. By passing throughThe laser terminals on the satellites and the neighboring satellites establish ISLs. By l i,j Representing satellite v i And v j Inter-satellite link with inter-satellite communication via laser terminals, and l i,j ∈E。
The in-track ISLs may remain, but the inter-track ISLs in the polar region are temporarily broken, and the chain is reestablished after exiting the polar region. An orbit seam exists between adjacent orbits with opposite satellite motion directions, and the cost of building a chain through the orbit seam is high, so the invention assumes that the orbit seam does not build a chain. In addition, two satellites in adjacent orbits will exchange their relative positions after passing through the polar region, forming a twisted manhattan network as shown in fig. 2, at (a) on the left side of fig. 2, converting the topology of the upper half rotated 180 degrees at (a) on the left side of fig. 2 into a pattern at (b) on the right side of fig. 2. The polar orbit LEO satellite network has a fixed two-dimensional Mash structure, and the dynamic property of the LEO satellite network is mainly determined by the fact that the on-off of inter-orbit ISLs caused by polar regions and the high error rate of a laser terminal caused by solar interference cannot build a chain.
V ES E V represents the set of ground satellites connected to the gateway station via the feeder link. Floor satellite v i Feed link W which can be established with gateway station i . Each satellite has 16 fixed directional spot beams for communication with subscribers and establishes a feeder link with the gateway station ES via the antenna. A plurality of gateway stations are distributed globally, each gateway station has k antennas, and feed links can be established with k satellites simultaneously. The satellite can only download data to the gateway station within the line of sight of the gateway station ES, referred to as a download time window. The user data received by each satellite in the network follows a poisson distribution. Since the satellite performs a motion with a period of T, the LEO satellite network topology also changes periodically, and for ease of analysis, the invention divides the satellite operating period into time slots of equal length τ, so the time line can be denoted 0,1 τ,2 τ.
For any link l n Total capacity C n Can be expressed as
Wherein eta n ,
β n And W is n Respectively, spectral efficiency, multipath gain, frequency reuse factor, and bandwidth allocated for the link. Can calculate satellite v i Total capacity of feed link B i Because the inter-satellite links established by the laser terminals are attenuated by solar interference or other conditions, the total capacity L of the different inter-satellite links is the same although the allocated bandwidths are the same i,j Different, it can be calculated by the formula (1).
The instantaneous transmission rate of data can be expressed as r n ＝ρ n x n Wherein ρ, x n Packet size and instantaneous traffic (packets/sec) of the link, respectively. The present invention assumes that all packets in the network are the same size. Satellite v i Current feeder link instantaneous rate b i Inter-satellite link instantaneous rate of input and output data to and from port j ( j e 1,2,3, 4)
And->
Can be calculated by the formula (1) and any link l n The instantaneous transmission rate of data needs to satisfy r n <C n 。
To obtain satellite v i Data transmission rates required for transmission to gateway stations, at satellite v i In the absence of congestion or failure of all inter-satellite links, i.e
Data transfer rate offloaded over feeder link is
When l i -B i >At the time of 0, the temperature of the liquid,representing satellite v i Failure to offload all data to the gateway station can result in packet loss, otherwise, satellite v is described i The feed link has a margin in bandwidth, at which time the feed link data transmission rate b i ＝l i . The invention optimizes the aim of increasing the throughput of the network and fully utilizes the feed resources, namely
maxΣ i |l i -B i | (3)
The goal of the algorithm in the present invention is to maximize the sum of the differences in equation (4). For ease of analysis, simplicity. The present invention makes the following assumptions:
transmitting data packets with the same size between all satellites and between the satellites and the gateway station; under this assumption, the amount of data that the satellite needs to transmit to the gateway station may be represented as the number of data packets, which may be further represented by the link rate;
each satellite is provided with 4 laser terminals to establish inter-satellite links with adjacent 4 satellites in the same orbit and different orbits, and simultaneously is provided with a wireless signal transmitting and receiving terminal and a gateway station to establish feed links, and the links work in a simplex mode; and
the data transmission of the inter-satellite link and the feeder link is error-free.
Compared with a satellite network mainly unloading remote sensing data, the routing table calculation of the data packets by the broadband low-orbit satellite network relies on real-time residual bandwidth of inter-satellite links, and the change of the data transmission rate of the inter-satellite links is not perceived in time, so that a large amount of packet loss and congestion are caused. In order to effectively utilize the inter-satellite link to assist the feeder link in offloading data, it is first necessary to determine the traffic transmission requirements, including the source and destination and the data transmission rate at which the data to be offloaded to the gateway station is transmitted by the ISLs, and then calculate the forwarding path of the data packet between the ground satellites based on the requirements.
Let the
Representing real set, traffic demand matrix->
The element D (i, j) represents the data transmission rate required between a pair of satellites, and then the maximum flow minimum cost algorithm is used to calculate the link traffic matrix +_based on the matrix>
Where each element R (i, j) represents the data transmission rate after each inter-satellite link route. At the beginning of each time slot nτ, the network topology, and the link capacity, instantaneous transmission rate, etc. of each satellite inter-satellite link and feeder link are updated, as shown in fig. 3, at (a) on the left side of fig. 3. Black arrows, grey arrows and values thereof respectively represent satellite v i The instantaneous data transmission rate of the incoming and outgoing data streams over the inter-satellite link and the outgoing data streams over the feeder link and the maximum capacity of the link.
When l in the formula (4) i -B i <0, i.e. satellite v i Can additionally receive an offloaded data stream I Such satellite sets are V I . And the receivable data stream can be calculated by the formula (5) according to the inter-satellite link and feeder link capacities of the present satellite.
When l in the formula (5) i -B i >0, i.e. satellite v i Data stream l may need to be offloaded via ISLs O Such satellite sets are V O And according to the inter-satellite link resource capacity of the satellite, the data flow to be unloaded can be calculated by the formula (6).
After one round of updatingThe input and output streams of the satellite nodes are shown in the middle (b) of fig. 3 and the right (c) of fig. 3, respectively. The invention is based on satellite set V O And V I Each satellite l O And l I The magnitude of the value, the two satellites are concentrated in a one-to-one correspondence according to the order of the value from large to small, the two satellites are respectively used as the source and the destination of data transmission, and the min (l O ,l I ) As the source-to-destination demand traffic rate D (i, j). Thereby obtaining a traffic demand matrix D.
In one embodiment of the invention, the maximum flow minimum cost routing algorithm is shown in fig. 4, with two minimum cost paths between (9, 12) being P (9,8,7,12) and P (9,14,13,12), respectively, identified by gray arrows and lines in fig. 4. The maximum flow allowed between (9, 12) in fig. 4 includes four paths, the other more costly maximum flow paths being identified by black arrows and lines. The conventional maximum flow linear programming problem of multiple data flows has the following 3 problems that 1. The probability of data transmission on a shorter or longer path is the same, so that the transmission cost cannot be minimized; 2. loop-back may occur because transmission costs cannot be minimized; 3. the on-board computing resources are limited and even the LPs problem in a limited network scale is difficult to solve in time. The present invention is directed to solving the above problems by first proposing a method that allows planning shorter paths for larger traffic at the cost of the link distance bandwidth product (BD), minimizing transmission costs and preventing loop-back. And secondly, sub-graph constraint is carried out on the data flow in each pair of source and destination according to the energy and the computing resource, namely, the linear programming of the data flow can only be carried out in the corresponding sub-graph, thereby greatly reducing the operation complexity. Two linear programming problems of sub-graph constraints and maximum flow minimum cost will be described below.
In the satellite network topology graph G (V, E), the traffic demand matrix obtained by the above
The invention aims to calculate a subgraph G with distance constraint c (V c ,E c ) E G (V, E). First, dijkstra's shortest path algorithm is used to determine the area of the satellite (how this area is divided into temporary areasNot discussed in detail) all nodes compute shortest paths to other nodes in the region and initialize the data flow in the source/destination pair (s, d) to NULL by an algorithm. The algorithm traverses other intermediate nodes in the area, represents the hop count of the (s, d) shortest path by M (s, d), and takes a proper hop count threshold HT. If the intermediate node V meets M (s, V) +M (V, d) +M (s, d) +HT, adding the node V and four inter-star links thereof into the node set V of the subgraph c Sum edge set E c Is a kind of medium. Once sub-graph G is calculated for each data stream c The maximum flow minimum cost routing algorithm can be linearly programmed.
By distance constraint of the data streams for each pair of sources/sinks (s, d), a corresponding sub-graph can be obtained, and the maximum data stream linear programming problem (lp#1) of multiple sources and sinks under the limitation of the sub-graph is represented as company (7):
Subject to:
wherein l c (e) Representing the traffic rate on edge e.
And b c (v) Representing the total traffic rate and feeder link traffic rate of node v flowing in and out over the inter-satellite link, respectively. D (D) c Representing the corresponding requested traffic in the traffic demand matrix. 7.1-7.3 in equation (7) are constraints on link capacity. 7.4-7.6 are constraints on the traffic balance in the network for each sub-graph. 7.7 constraining the rate per data stream not to exceed the demand. By solving this linear programming, a multi-source to multi-purpose maximum flow in the network can be obtained.
To achieve the minimum achievable routing cost, the second linear programming problem (lp#2) is as in equation (8).
min:y * (8)
Subject to:
Wherein Γ is c Representing the maximum flow rate of the flow c obtained by solving the maximum flow linear programming problem, V' =v-(s) c ,d c ). 8.1 in the above equation requires a fixed rate for each flow, derived from LP# 1. The remaining constraints are similar to the previous LP constraints. The objective function of the present invention is to have all the data flow rates on each side
The sum of the products of the link costs M (e) is minimal. The invention solves the two linear programming problems by adopting a greedy algorithm to obtain the maximum flow minimum cost route in the network.
After completion of the calculations of the previous few segments of a round, an iteration of the network topology update is required, as shown in fig. 5. To reduce the iteration turn and increase the convergence rate, if V I Satellite in collection I <Alpha, the satellite exits set V I As in fig. 5, the gray node changes to a white node. If V O Satellite in collection O =0, then the set V is also exited O Changing from gray nodes to white nodes. Residual V I And V O The middle node repeats the calculation process until V O Or V I The number of the intermediate nodes is 0, that is, all data streams can be smoothly transmitted to the gateway station or the full throughput of the feed resources reaches the maximum, and the algorithm ends the iterative process until the next time slot tau is restarted. The algorithm flow chart algorithm is shown in fig. 6.
To verify the performance of the Inter-satellite link Assisted Collaborative Data Downloading (CDD) algorithm proposed by the present invention, the present invention was simulated using the Systems Tool Kit (STK) developed by AGI company (Analytical Graphics, inc.). The present invention compares the difference in performance of the proposed IACD algorithm with the conventional Genetic algorithm.
In the simulation experiment, the invention selects a representative Walker delta, globalstar constellation. In this constellation, there are 8 orbital planes, each orbital plane has 6 satellites, and the angular distance between the planes is 60 °. The orbit period 6840 minutes and the orbit tilt angle 52 °. The Globalstar satellite configures a laser terminal with a bandwidth of 10GHz for ISL communication and a wireless terminal with a bandwidth of 1GHz for ES communication. Suppose the simulation starts at UTC time 2021, 6, 27, 12:00:00, then 2021, 6, 27, 13:54:00UTC stops. ES is located in Shanghai city, latitude 31:53 deg. longitude 122:12 deg..
The present invention assumes that the amount of data received by the satellite from the user satisfies the poisson distribution (μ). First, in fig. 7 and 8, the present invention compares the throughput and time delay of the proposed algorithm (CDD) and Genetic algorithm from the total network load of 40% ES feeder link capacity to the total network load of 120% ES feeder link capacity by changing the flow average of poisson distribution, wherein the throughput is defined as the ratio of the actual data volume to the total data volume to be downloaded, and the end-to-end time delay is defined as the time interval between the uploading of a data packet to the satellite network and the receiving of the data packet from the ground gateway station. In fig. 9 and 10, the present invention compares the delay profiles of the three algorithms at 40% and 120% network load, respectively. From the simulation results, it can be seen that:
1) And as the traffic load changes, the throughput performance of the method remains stable and can unload almost all traffic completely before the load reaches 100% (see fig. 6). The genetics algorithm starts to drop in throughput with increasing network load. This is because part of the feeder links still need to receive a large amount of traffic to be offloaded in case of bandwidth reduction caused by interference of the feeder links, thereby generating buffer overflow and packet loss. The algorithm of the invention uses inter-satellite links to assist data unloading, thereby effectively improving network throughput.
2) Even when the network load reaches 120% of the total capacity of the feeder link, the end-to-end average delay of the algorithm proposed by the invention is still around 0.6s (as shown in fig. 7). Whereas the Genetic algorithm average delay reaches 0.9s, which means that a significant fraction of the packet delay will exceed its lifetime and thus create packet losses. When the network load exceeds 100%, the Genetic algorithm delay increases by a larger magnitude. This is more apparent from the time delay profile in fig. 8 and 9. When the network load is low, almost all the packet end-to-end delays in the algorithm are distributed between 0.1 and 0.3s, while when the load is heavy (120%), most of the packet delays in the algorithm are still lower than 0.7s, and the genetics algorithm has nearly 50% and more than 0.9s respectively. This is because the accumulation of a large number of packets on a low bandwidth link results in a dramatic increase in queuing delay, and the present algorithm will minimize the end-to-end delay of the packets by sending the data to be offloaded to satellites with larger feeder link bandwidths.
The invention considers a method for assisting in unloading feed data by using inter-satellite links, which allows satellites to send data to be unloaded to a ground satellite with residual bandwidth through ISLs, and fully utilizes feed bandwidth resources. The invention addresses the problem of MFMC linear programming with graph constraints and develops iterative algorithm CDD to maximize system throughput and minimize data transmission delay. The simulation work of the invention is carried out through Systems Tool Kit (STK), and the simulation result shows that the CDD of the algorithm provided by the invention is superior to the traditional Genetic algorithm in throughput and time delay. The invention focuses on data transmission between ground satellites.
In summary, the foregoing embodiments describe different configurations of the inter-satellite data transmission method in detail, and of course, the present invention includes, but is not limited to, configurations listed in the foregoing embodiments, and any content that changes based on the configurations provided in the foregoing embodiments falls within the scope of protection of the present invention. One skilled in the art can recognize that the above embodiments are illustrative.
In the present specification, each embodiment is described in a progressive manner, and each embodiment is mainly described in a different point from other embodiments, and identical and similar parts between the embodiments are all enough to refer to each other. For the system disclosed in the embodiment, the description is relatively simple because of corresponding to the method disclosed in the embodiment, and the relevant points refer to the description of the method section.
The above description is only illustrative of the preferred embodiments of the present invention and is not intended to limit the scope of the present invention, and any alterations and modifications made by those skilled in the art based on the above disclosure shall fall within the scope of the appended claims.
Claims (1)
1. An inter-satellite data transmission method, comprising:
the inter-satellite link is utilized to assist in unloading feed data, and the satellite transmits data to be unloaded to a ground satellite with residual bandwidth through the inter-satellite link so as to utilize feed bandwidth resources; and
according to the MFMC linear programming constrained by the band diagram, developing an iterative algorithm and a date downloading algorithm to maximize the system throughput and minimize the data transmission delay;
the satellite network consists of N orbits, and each orbit comprises M satellites;
the LEO satellite network is represented by a graph g= (V, E), where V represents a set of nodes and E represents a set of inter-satellite links, including inter-satellite links and feeder links;
establishing an inter-satellite link through a laser terminal on a satellite and a neighbor satellite;
by l i,j Representing satellite v i And v j Inter-satellite link with inter-satellite communication via laser terminals, and l i,j ∈E；
Inter-orbit inter-satellite links are kept all the time, and are temporarily disconnected in a polar region, and the links are reestablished after leaving the polar region;
two satellites on adjacent orbits pass through the polar region and then exchange relative positions to form a twisted Manhattan network, and the upper half part of the twisted Manhattan network is rotated by 180 degrees;
the polar orbit LEO satellite network has a fixed two-dimensional Mash structure, and the dynamic property of the LEO satellite network is determined by the fact that the link between the orbits caused by polar regions is on-off, and the error rate of a laser terminal caused by sunlight interference is too high to build a link;
V ES e, V represents a set of ground satellites connected with the gateway station through a feed link;
floor satellite v i Establishing a feed link W with a gateway station i ；
Each satellite has 16 spot beams with fixed directions for communication with users, and a feed link is established through an antenna and a gateway station ES;
a plurality of gateway stations are distributed globally, each gateway station is provided with k antennas, and feed links are established with k satellites at the same time;
the satellite downloads data to the gateway station in the sight range of the gateway station ES, which is called a downloading time window; the satellite operating period is divided into time slots of equal size and length τ, the time lines being denoted 0,1 τ,2 τ,..;
for any link l n Total capacity C n Represented as
Wherein the method comprises the steps of
And W is n Respectively representing the frequency spectrum efficiency, the multipath gain, the frequency multiplexing coefficient and the bandwidth allocated by the link;
calculating satellite v i Total capacity of feed link B i ；
The instantaneous transmission rate of data is denoted as r n ＝ρ n x n Wherein ρ, x n Instantaneous traffic (packets/sec) for the packet size and link, respectively;
in satellite v i In the absence of congestion or failure of all inter-satellite links, i.e
Data transfer rate offloaded over feeder link is
When l i -B i >0, representing satellite v i Failure to offload all data to gateway station, packet loss occurs, otherwise satellite v is indicated i The feed link has a margin in bandwidth, at which time the feed link data transmission rate b i ＝l i The method comprises the steps of carrying out a first treatment on the surface of the Make full use of the feed resources
max∑ i |l i -B i | (3)
Transmitting data packets with the same size between all satellites and between the satellites and the gateway station;
the amount of data that the satellite needs to transmit to the gateway station is expressed as the number of data packets, the number of data packets being expressed in terms of link rate;
each satellite is provided with 4 laser terminals to establish inter-satellite links with adjacent 4 satellites in the same orbit and different orbits, and simultaneously is provided with a wireless signal transmitting and receiving terminal and a gateway station to establish feed links, and the links work in a simplex mode;
the data transmission of the inter-satellite link and the feeder link is error-free;
firstly, determining and obtaining a flow transmission requirement, including a source and a destination for transmitting data to be unloaded to a gateway station and a data transmission rate through an inter-satellite link, and then calculating a forwarding path of a data packet between landing satellites according to the requirement;
let the
Representing real set, traffic demand matrix->
Each element D (i, j) of (a) representsThe data transmission rate required between a pair of satellites is calculated by using the maximum flow minimum cost algorithm according to the matrix to obtain a link flow matrix
Wherein each element R (i, j) represents the data transmission rate after each inter-satellite link route;
updating the network topology structure and the link capacity of each satellite inter-satellite link and feeder link when each time slot nτ starts, and the instantaneous transmission rate parameters;
when in the above formula I i -B i <0, i.e. satellite v i Capable of additionally receiving an offloaded data stream l I Such satellite sets are V I The method comprises the steps of carrying out a first treatment on the surface of the And according to the inter-satellite link and feeder link capacity of the satellite, calculating a receivable data stream by the following formula;
when in the above formula I i -B i >0, i.e. satellite v i Offloading data flow/via inter-satellite link O Such satellite sets are V O According to the inter-satellite link resource capacity of the satellite, calculating the data flow to be unloaded according to the following formula;
according to satellite set V O And V I Each satellite l O And l I The magnitude of the value, the two satellites are concentrated in a one-to-one correspondence according to the order of the value from large to small, the two satellites are respectively used as the source and the destination of data transmission, and the min (l O ,l I ) As the source-to-destination demand traffic rate D (i, j); thereby obtaining a flow demand matrix D;
at the cost of the link distance bandwidth product (BD), allowing shorter paths to be planned for larger traffic, minimizing transmission costs and preventing loop-backs;
sub-graph constraint is carried out on the data flow in each pair of sources and purposes according to energy and computing resources, namely linear programming of the data flow can only be carried out in the corresponding sub-graph, so that the operation complexity is reduced;
in the satellite network topology graph G (V, E), the obtained traffic demand matrix is used for generating a traffic demand matrix
Computing subgraph G with distance constraints c (V c ,E c )∈G(V,E)；
Calculating shortest paths from all nodes in a ground satellite area to other nodes in the area by using a Dijkstra shortest path algorithm, initializing a group of candidate nodes and candidate edge sets into NULL by using data flows in a source/destination pair (s, d);
traversing other intermediate nodes in the area, using M (s, d) to represent the hop count of the (s, d) shortest path, and taking a proper hop count threshold HT;
if the intermediate node V meets M (s, V) +M (V, d) +M (s, d) +HT, adding the node V and four inter-star links thereof into the node set V of the subgraph c Sum edge set E c In (a) and (b);
computing subgraph G for each data stream c Then, carrying out linear programming on a maximum flow minimum cost routing algorithm;
by performing distance constraint on the data streams of each pair of sources/sinks (s, d), a corresponding sub-graph is obtained, and the maximum data stream linear programming problem of multiple sources and multiple sinks under the limitation of the sub-graph is represented as formula (7):
Subject to:
wherein l c (e) Representing the flow rate on edge e;
and b c (v) Respectively representing the total flow rate of the node v flowing in and out through the inter-satellite links and the feed link flow rate; d (D) c Representing corresponding request flow in the flow demand matrix; in the formula (7), the constraint on the link capacity is shown as (7.1) - (7.3); (7.4) - (7.6) are constraints on the traffic balance in the network for each sub-graph; (7.7) constraining each data stream to a rate not exceeding the demand; the maximum flow from multiple sources to multiple purposes in the network can be obtained by solving the linear programming;
to obtain the minimum achievable routing cost, a second linear programming problem is as in equation (8);
min：y * (8)
Subject to:
wherein Γ is c Representing the maximum flow rate of the flow c obtained by solving the maximum flow linear programming problem, V' =v-(s) c ,d c ):
The constraints (8.2) - (8.5) in equation (8) are similar to the previous constraints (7.3) - (7.6);
the objective function is to have all the data flow rates on each side
The sum of the products of the link cost M (e) is minimum;
solving the two linear programming problems by adopting a greedy algorithm to obtain a maximum flow minimum cost route in the network;
after more than one round of calculation is completed, updating and iterating the network topology, and accelerating the convergence speed for reducing iteration rounds, if V I Satellite in collection I <Alpha, the satellite exits set V I The method comprises the steps of carrying out a first treatment on the surface of the If V O Satellite in collection O =0, then the set V is also exited O The method comprises the steps of carrying out a first treatment on the surface of the Residual V I And V O The middle node repeats the calculation process until V O Or V I The number of the intermediate nodes is 0, all data streams can be smoothly transmitted to the gateway station or the full throughput of the feed resources reaches the maximum, and the iteration process is ended until the next time slot tau starts the next round of operation.
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