A multi-layer satellite network transmission demand unloading method and system

Abstract

The present invention discloses a multi-layer satellite network transmission demand unloading method and system, belonging to the field of information communication technology. The method comprises: a LEO satellite receives a data packet of a ground user through a satellite-to-ground link, and transmits the data packet to a target LEO satellite through a LEO intersatellite link; when the transmission demand exceeds its capacity, the LEO satellite establishes an interlayer link with a corresponding MEO satellite according to its own transmission capacity and the size of the transmission demand, and unloads the redundant transmission demand; wherein each LEO satellite independently selects a MEO satellite to establish an interlayer link, and the problem of LEO satellite accessing a MEO satellite is modeled as an overlapping alliance formation game; the present invention transmits data exceeding its own transmission capacity to the MEO satellite through the interlayer link, so that the transmission demands and transmission capabilities of the LEO satellite and the MEO satellite are matched, and the waste of transmission resources and the occurrence of congestion are avoided.

Description

Technical Field

[0001] The invention relates to a multi-layer satellite network transmission demand unloading method and system, belonging to the field of information communication technology. Background Art

[0002] Satellite communications have the ability to provide communication services to ground users at any location. The multi-layer satellite network, which is mainly composed of low-orbit (LEO) satellites and medium-orbit (MEO) satellites, combines the advantages of satellite networks in different orbits. Compared with single-layer networks, it has a more flexible architecture and higher communication capacity. In each layer of the satellite network in the multi-layer satellite network, there are inter-satellite links to realize the networking of satellites in this layer. Through the inter-satellite links, data forwarding between satellites in the layer can be realized. At the same time, inter-layer links can also be established between satellites in different layers. Through the inter-layer links, network management signaling and user data transmission can be carried out.

[0003] Some existing methods use a method of decoupling data transmission from network management, with the upper satellite being mainly responsible for network management (mobility management, routing management, etc.), and the lower satellite being mainly responsible for user data transmission. When the lower satellite is congested due to excessive transmission demand, a detour is used to avoid congestion. Although this method realizes distributed management of the network and is easy to implement, it wastes transmission resources on the upper satellite. As user data increases, congestion of the lower transmission satellite becomes very common. Therefore, this patent proposes a low-complexity method for establishing an inter-layer link between LEO satellites and MEO satellites. The LEO satellite joins the alliance of the corresponding MEO satellite in a distributed manner, effectively unloading the excess transmission demand on the LEO satellite, and utilizing the excess transmission capacity on the upper satellite to reduce the mismatch between the transmission demand and transmission capacity of the entire network. Summary of the invention

[0004] The purpose of the present invention is to overcome the deficiencies in the prior art and provide a multi-layer satellite network transmission demand unloading method and system, which transmits data exceeding its own transmission capacity to a MEO satellite through an inter-layer link, thereby matching the transmission requirements and transmission capacity of the LEO satellite and the MEO satellite, avoiding the waste of transmission resources and the occurrence of congestion.

[0005] To achieve the above object, the present invention is implemented by adopting the following technical solutions:

[0006] In a first aspect, the present invention provides a method for offloading multi-layer satellite network transmission requirements, comprising:

[0007] The LEO satellite receives data packets from ground users via satellite-to-ground links and transmits the data packets to the destination LEO satellite via LEO intersatellite links;

[0008] When the transmission demand exceeds its capacity, the LEO satellite establishes an inter-layer link with the corresponding MEO satellite based on its own transmission capacity and the size of the transmission demand and unloads the excess transmission demand;

[0009] Among them, each LEO satellite independently selects a MEO satellite to establish an inter-layer link, and the problem of LEO satellite access to MEO satellite is modeled as an overlapping coalition formation game.

[0010] Furthermore, the LEO satellite can also receive and forward data packets from adjacent satellites, and send them to the adjacent satellites with the same probability.

[0011] Furthermore, the problem of LEO satellite accessing MEO satellite is modeled as an overlapping alliance formation game, including:

[0012] Define the set of non-empty subsets of the set of LEO satellites that are considered to be overlapping federation structures;

[0013] In an overlapping alliance structure, each LEO satellite is allowed to independently choose to join an alliance based on its strategy;

[0014] Set the preference rule so that for any LEO satellite, the satellite has a tendency to leave the original alliance and join another alliance;

[0015] The judgment condition of alliance stability is established. When any LEO satellite cannot unilaterally change its alliance choice to improve its benefits according to the set preference rules, the alliance is judged to be in a stable state.

[0016] Furthermore, the LEO satellite establishes an inter-layer link with the corresponding MEO satellite according to its own transmission capacity and the size of the transmission demand. The specific formula is as follows:

[0017]

[0018]

[0019] Among them, the collection Includes MEO satellites in the alliance and LEO satellite collection represents the mismatch between the transmission capacity and transmission demand of alliance j, N m represents the number of MEO satellites, A is the inter-layer link matrix between LEO satellites and MEO satellites, and D k (t) and C k (t) represent the transmission demand and transmission capacity of satellite k at time t respectively.

[0020] Furthermore, in an overlapping alliance structure, each LEO satellite is allowed to independently choose to join an alliance according to its strategy. The specific formula is as follows:

[0021]

[0022] in, Indicates LEO satellite Forming a new alliance, p i (t) and N i They are the transmission power of LEO satellites and the number of MEO satellites joining the alliance. The transmission power of LEO satellites is evenly distributed to each connected MEO satellite. and Represents LEO satellites With MEO satellite and Inter-layer link transmit power.

[0023] Furthermore, in the step of setting the preference rule, for any LEO satellite LEO Satellites Prefer to leave the original alliance Join another alliance If and only if the following holds:

[0024]

[0025] Compared with the Alliance j1LEO satellite Prefer alliance j2, and represents the LEO satellites in the original alliance j2 and j1, Indicates LEO satellite Join the J2 Alliance, Indicates LEO satellite Leave alliance j1. Indicates the mismatch between the original J2 Alliance's transmission capabilities and transmission requirements. It indicates the mismatch between the transmission capacity and transmission demand of the original J1 alliance. Indicates LEO satellite The mismatch between the alliance's transmission capacity and transmission demand after joining J2. Indicates LEO satellite The mismatch between the alliance's transmission capacity and transmission demand after leaving J1;

[0026] LEO Satellites The utility function of is defined as:

[0027]

[0028] in, Indicates LEO satellite Access to MEO satellite The utility function when It indicates the mismatch between the transmission capacity and transmission demand of the original J1 alliance. Indicates LEO satellite The mismatch between the alliance's transmission capacity and transmission demand after leaving J1.

[0029] Furthermore, when any LEO satellite cannot unilaterally change its alliance selection to improve its benefits according to the set preference rules, the alliance is determined to be in a stable state, and the expression is as follows:

[0030]

[0031] Among them, U sk and U sk′ Represents LEO satellites The original alliance selection and the new alliance selection, V i (U sk ,U sk- ) indicates LEO satellite In the original coalition utility function, V i (U sk′ ,U sk- ) indicates LEO satellite In the utility function of the new coalition, U sk- In addition to LEO satellites Alliance options for other LEO satellites.

[0032] In a second aspect, a multi-layer satellite network transmission demand offloading system is characterized by comprising:

[0033] Multiple LEO satellites are used to receive data packets from ground users through satellite-to-ground links, transmit data packets to the destination LEO satellite through LEO inter-satellite links, and establish inter-layer links with corresponding MEO satellites and unload excess transmission demands according to their own transmission capabilities and the size of transmission demands when the transmission demand exceeds their capabilities; each LEO satellite can independently select a MEO satellite to establish an inter-layer link, and this process is achieved by using a coalition formation game;

[0034] At least one MEO satellite is used to receive the transmission demand offloaded from the LEO satellite and perform the transmission.

[0035] Furthermore, the LEO satellite can also receive and forward data packets from adjacent satellites, and send them to the adjacent satellites with the same probability.

[0036] Furthermore, the LEO satellite transmits the data to be offloaded to the connected MEO satellites on an average basis.

[0037] Compared with the prior art, the present invention has the following beneficial effects:

[0038] 1. Joint congestion avoidance in multi-layer satellite networks: This method proposes to use the transmission capacity of the MEO layer satellite in the multi-layer satellite network to offload the remaining transmission capacity in the LEO layer satellite to the MEO satellite for transmission. Compared with the congestion avoidance method that only uses the MEO layer satellite for network management and LEO layer traffic bypass in the multi-layer satellite network, it effectively utilizes the transmission capacity in the network and effectively avoids network congestion.

[0039] 2. Distributed solution based on alliance formation game: The method proposed in the present invention is a distributed solution, in which LEO satellites join corresponding alliances according to their current transmission capabilities and transmission requirements without the need for additional signaling interactions.

[0040] 3. This scheme designs a minimum mismatch criterion. When the sum of the mismatches of the new and old alliances decreases, the LEO satellite will join the new alliance. Compared with the selfish criterion and the Pareto criterion, this criterion can achieve a lower mismatch of the entire network. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] Figure 1 It is a flow chart of a multi-layer satellite network transmission demand unloading method provided by an embodiment of the present invention;

[0042] Figure 2 is a schematic diagram of an inter-layer link allocation algorithm based on OCFG provided in an embodiment of the present invention;

[0043] Figure 3 is a schematic diagram of algorithm convergence provided by an embodiment of the present invention;

[0044] Figure 4 is a performance comparison of algorithms provided by an embodiment of the present invention: a schematic diagram showing the relationship between the total network mismatch degree and the number of LEO satellites;

[0045] Figure 5 1 is a schematic diagram of the relationship between the algorithm performance comparison provided by an embodiment of the present invention and the total network mismatch degree and the number of MEO satellites. DETAILED DESCRIPTION

[0046] The present invention will be further described below in conjunction with the accompanying drawings. The following embodiments are only used to more clearly illustrate the technical solution of the present invention, and cannot be used to limit the protection scope of the present invention.

[0047] Embodiment 1: This embodiment introduces a multi-layer satellite network transmission demand unloading method, including:

[0048] The LEO satellite receives data packets from ground users via satellite-to-ground links and transmits the data packets to the destination LEO satellite via LEO intersatellite links;

[0049] When the transmission demand exceeds its capacity, the LEO satellite establishes an inter-layer link with the corresponding MEO satellite based on its own transmission capacity and the size of the transmission demand and unloads the excess transmission demand;

[0050] Among them, each LEO satellite independently selects a MEO satellite to establish an inter-layer link, and the problem of LEO satellite access to MEO satellite is modeled as an overlapping coalition formation game.

[0051] The application process of the multi-layer satellite network transmission demand offloading method provided in this embodiment specifically involves the following steps:

[0052] In a multi-layer satellite network, due to the limited transmission capacity of LEO satellites, there may be a situation where the data that the LEO satellite needs to transmit to cover the communication hotspot area does not match its transmission capacity. This causes a large number of data packets to accumulate at the LEO satellite, resulting in high queuing delays, which seriously affects the network service performance. Compared with LEO satellites, MEO satellites have stronger transmission capabilities and longer single-hop transmission distances. Therefore, the congestion problem of the LEO satellite network can be effectively solved with the help of the transmission capacity of MEO satellites. When the transmission capacity of the LEO satellite does not match the transmission demand, the data that exceeds its own transmission capacity is transmitted to the MEO satellite through the inter-layer link, so that the transmission requirements and transmission capabilities of the LEO satellite and the MEO satellite are matched, avoiding the waste of transmission resources and the occurrence of congestion. The alliance formation game can enable participants to form an alliance in a distributed manner so that the overall utility can be better. This patent proposes a method for establishing an inter-layer link and unloading traffic between MEO satellites and LEO satellites based on the alliance formation game applied to a multi-layer satellite network. The basic principle is as follows:

[0053] 1. Channel Model

[0054] The model designed by this patent is divided into the same-layer inter-satellite link model (inter-satellite link) and the different-layer inter-satellite link model. The satellite works in the outer space of the earth. The inter-satellite link is mainly affected by free space loss and thermal noise, which belongs to free space loss. Therefore, the channel gain of satellites n and m in time slot t can be expressed as:

[0055]

[0056] Where c is the speed of light, k B is the Boltzmann constant, is the thermal noise factor in Kelvin (K), f nm , G nm and B nm are carrier frequency, antenna gain and transmission bandwidth, is the inter-satellite distance. Assuming that the transceiver antennas of the two satellites involved in the inter-satellite link can be aligned in the direction of maximum radiation, the achievable data rate of the inter-satellite link nm in time slot t is

[18] :

[0057]

[0058] Among them, p nm is the transmission power of satellite n, B nm is the transmission bandwidth, is the intersatellite link channel gain.

[0059] The working environment of the inter-layer link is similar to that of the inter-satellite link. In the present invention, the LEO satellite accesses the MEO satellite by frequency division multiplexing, so there is no interference between the LEO satellites. The channel modeling of the inter-layer link is similar to that of the inter-satellite link. The achievable data rate of the inter-layer link in time slot t is:

[0060]

[0061] Among them, B ij and p ij Respectively represent the transmission bandwidth and transmission power of the inter-layer link, is the inter-layer link channel gain.

[0062] 2. Packet arrival model

[0063] The user data transmission process in the multi-layer satellite network of this patent is as follows: the ground user sends the data packet to the LEO satellite through the satellite-to-ground link, the LEO satellite transmits it to the destination LEO satellite through the LEO inter-satellite link, and then the destination satellite transmits it to the corresponding ground user through the satellite-to-ground link. If the transmission demand of the LEO satellite is greater than its transmission capacity, the LEO satellite establishes an inter-layer link with the MEO satellite to offload part of the transmission demand to the MEO satellite for transmission. The data received from the ground user is subject to the parameter λ i Poisson distribution of :

[0064]

[0065] Due to the uneven distribution of ground users, λ i The size of is related to the current location of the satellite. When the satellite passes through an area with active communication activities, i The value is larger, otherwise it is smaller. Indicates LEO satellite Newly arrived user data.

[0066] In addition to receiving data packets from ground users, LEO satellites also receive data packets transmitted from neighboring satellites. Assuming that user data is sent to any location with equal probability, the data packets of LEO satellites will be sent to neighboring satellites with the same probability. In this patent, the average amount of data sent by each LEO satellite to neighboring satellites is D k (t) (k = 1, 2, 3, 4 represents different neighboring satellites), then the data received by the LEO satellite from an adjacent LEO satellite is D k (t) / 4, therefore, the present invention defines LEO satellite Amount of data received from adjacent LEO satellites for:

[0067]

[0068] Among them, D k is the amount of data to be transmitted by the neighboring LEO satellite, k refers to different neighboring satellites, R k (t) is the transmission rate of the LEO satellite intersatellite link, T s The length of each time slot, min{} means taking the minimum value of the two.

[0069] At time t, the LEO satellite The total amount of data that needs to be transferred It mainly includes three parts, which can be expressed as:

[0070]

[0071] in, It is the LEO satellite in the previous time slot The remaining data, when t = 1 Newly sent to satellite for ground users data, It is transmitted to the satellite by the adjacent LEO satellite. data.

[0072] Similarly, at time tMEO satellite Data packets to be transmitted It can be expressed as:

[0073]

[0074] in, It is the MEO satellite in the previous time slot The remaining data, when t = 1, Is with MEO satellite Data sent from LEO satellites that establish inter-layer links, It is sent by the adjacent MEO satellite to the MEO satellite. data.

[0075] In this patent, LEO satellite The data that needs to be offloaded is evenly transmitted to the connected MEO satellites. The data received from LEO satellites is related to the connected LEO satellites and their number, which can be expressed as:

[0076]

[0077] in, is the LEO satellite at time slot t The amount of data that needs to be offloaded to the MEO satellite layer. ij (t) is a binary variable. With MEO satellite When establishing an inter-layer link, a ij (t) is 1, otherwise it is 0. is the transmission rate of the inter-layer link, T s The length of each time slot, MEO satellite Amount of data received from adjacent MEO satellites for:

[0078]

[0079] D k′ is the amount of data to be transmitted by the neighboring MEO satellite, k′ refers to different neighboring satellites, R k′ (t) is the transmission rate of the MEO satellite intersatellite link, T s The length of each time slot, min{} means taking the minimum value of the two.

[0080] 3. Satellite transmission capability model

[0081] With the application of large-scale multiple-input multiple-output and non-orthogonal multiple access technologies in satellite communications, the capacity of the satellite-to-ground link has been greatly improved. The present invention assumes that congestion only occurs during ISL transmission. Therefore, the transmission capacity of the satellite is related to the capacity of its four ISLs. Therefore, the time slot tLEO satellite Transmission capacity for:

[0082]

[0083] Among them, R k is the achievable data rate of the kth LEO satellite ISL, T s is the length of each time slot. Similarly, the time slot tMEO satellite Transmission capacity for:

[0084]

[0085] R k′ is the achievable data rate of the k′th MEO satellite ISL, T s is the length of each time slot.

[0086] 4. Method for offloading LEO satellite transmission demand in multi-layer satellite network

[0087] This method enables LEO satellites and MEO satellites in a multi-layer satellite network to establish inter-layer links and unload the redundant transmission requirements on the LEO satellites, so as to minimize the mismatch between the transmission capacity and transmission requirements of the entire network satellites in each time slice (hereinafter referred to as mismatch), where the mismatch and objective function are defined as:

[0088]

[0089]

[0090]

[0091] C3:a ij (t)∈{0,1}

[0092]

[0093]

[0094] Among them, ψ in C1 and C2 LEO and ψ MEO The mismatch degree of LEO satellite layer and MEO satellite layer is defined respectively. C3 defines the binary indicator variable a ij (t), a ij (t) is the i-th row and j-th column element of the binary indicator variable matrix A. With MEO satellite When connected through inter-layer links ij (t)=1, otherwise a ij (t) = 0. C4 and C5 are the constraints on the number of MEO satellites that each LEO satellite can access and the number of LEO satellites that each MEO satellite can serve. m is the maximum number of LEO satellites that a MEO satellite can serve, L mis the maximum number of MEO satellites that a LEO satellite can access. Problem P takes the number of inter-layer links that a LEO satellite can simultaneously maintain and the service capacity of a MEO satellite as constraints. By optimizing the connection between the inter-layer links of LEO satellites and MEO satellites, the mismatch of the entire network can be minimized. The specific solution ideas are as follows: Figure 1 shown.

[0095] 2.1. Transmission demand offloading optimization: To solve problem P, LEO satellites need to establish inter-layer links with corresponding MEO satellites and offload excess transmission demand according to their own transmission capacity and transmission demand. The selection of each LEO satellite will not only affect its own mismatch, but also the mismatch between other MEO satellites and LEO satellites. It is necessary to design a distributed strategy so that each LEO satellite can independently select MEO satellites to establish inter-layer links and offload transmission demand without incurring additional signaling burden. This method uses alliance formation game to achieve this process.

[0096] The problem of LEO satellite access to MEO satellite is modeled as an Overlapping Coalition Formation Game (OCFG) to minimize the mismatch between the satellite transmission capacity and transmission demand of the entire network. The optimization problem can be expressed as:

[0097]

[0098]

[0099] Among them, the collection Includes MEO satellites in the alliance and LEO satellite collection represents the mismatch between the transmission capacity and transmission demand of alliance j, N m represents the number of MEO satellites, A is the inter-layer link matrix between LEO satellites and MEO satellites, and D k (t) and C k (t) represent the transmission demand and transmission capacity of satellite k at time t respectively.

[0100] Definition 1 (Overlapping coalition formation game) The overlapping coalition structure is the set of non-empty subsets of the LEO satellite set. l Divided into a number of overlapping alliances in, Representative access to MEO satellite The collection of LEO satellites, N m′ Indicates the total number of LEO satellites accessing MEO satellites, N m′ <N m Indicates that LEO satellites will not access certain MEO satellites.

[0101] In OCFG, each LEO satellite independently selects an alliance to join based on its own strategy, ultimately achieving the minimum mismatch between the transmission demand and transmission capacity of the entire network of satellites. Therefore, the OCFG criteria are defined as:

[0102]

[0103] in, Indicates LEO satellite Forming a new alliance, p i (t) and N i are the transmission power of LEO satellites and the number of MEO satellites joining the alliance. The transmission power of LEO satellites is evenly distributed to each connected MEO satellite. ij (t) indicates LEO satellite With MEO satellite Inter-layer link transmit power.

[0104] In order to minimize the mismatch between the satellite transmission capacity and transmission demand of the whole network, the minimum mismatch criterion is proposed, and the LEO satellite Definition of utility function:

[0105] Definition 2 (minimum mismatch criterion): For any LEO satellite LEO Satellites Prefer to leave the original alliance Join another alliance If and only if the following holds:

[0106]

[0107] Compared with the Alliance j1LEO satellite Prefer alliance j2, and represents the LEO satellites in the original alliance j2 and j1, Indicates LEO satellite Join the J2 Alliance, Indicates LEO satellite Leave alliance j1. Indicates the mismatch between the original J2 Alliance's transmission capabilities and transmission requirements. It indicates the mismatch between the transmission capacity and transmission demand of the original J1 alliance. Indicates LEO satellite The mismatch between the alliance's transmission capacity and transmission demand after joining J2. Indicates LEO satellite The mismatch between the alliance's transmission capacity and transmission demand after leaving J1;

[0108] LEO Satellites The utility function of is defined as:

[0109]

[0110] Definition 3 (Stable Alliance Formation) If any LEO satellite cannot unilaterally change its alliance choice to improve its benefits according to the relevant preference relationship, then the alliance is stable. That is:

[0111]

[0112] Among them, U sk and U sk′ Represents LEO satellites The original alliance selection and the new alliance selection, V i (U sk ,U sk- ) indicates LEO satellite In the original coalition utility function, V i (U sk′ ,U sk- ) indicates LEO satellite In the utility function of the new coalition, U sk- In addition to LEO satellites The coalition selection of other LEO satellites. Theorem 1: OCFG based on the minimum mismatch criterion can reach Nash equilibrium and is the suboptimal solution to problem P2.

[0113] Proof: When L m =1, the alliance of LEO satellites is divided into non-overlapping alliances. The Exact Potential Game (EPG) is introduced to prove that the CFG based on the proposed minimum mismatch criterion can form a stable non-overlapping alliance division. The definition of EPG is given:

[0114] Definition 4 (Exact Potential Game): If there exists a potential function satisfying equation (18), then the game is an EPG.

[0115]

[0116] The potential energy function φ in this paper is defined as:

[0117]

[0118] When LEO satellite Leaving the Alliance Join the Alliance When , the change of potential energy function is:

[0119]

[0120] At the same time, LEO satellites The change in the utility function is:

[0121]

[0122] Obviously you can get Therefore, the OCFG is an EPG.

[0123] According to the definition of EPG, the OCFG has at least one pure Nash equilibrium (NE) point. Since the number of LEO satellites and MEO satellites is limited, and each change in the alliance will reduce the mismatch between the transmission demand and transmission capacity of the entire network of satellites, the game will eventually converge to the NE point and reach stability. Because the potential energy function is the objective function of problem P2, when the CFG is stable, the NE point is L m The suboptimal solution to problem P2 when =1.

[0124] When L m =2, belongs to the alliance LEO satellite Join or form a new alliance When , the change of potential energy function is:

[0125]

[0126] At the same time, LEO satellites The change in the utility function is:

[0127]

[0128] Obviously, we can get L m =2, Similarly, when L m >2, there are Therefore, when L m ≥2, the OCFG is an EPG and has at least one pure NE point. The number, transmission requirements, and transmission capacity of LEO and MEO satellites are limited, and when the alliance division changes, it will only happen if the mismatch of the relevant alliance decreases. Therefore, the game can eventually converge to the NE point and reach stability. Because the potential energy function is the objective function of problem P2, when the OCFG is stable, the NE point is L m ≥2 is the suboptimal solution to problem P2. In summary, for any L m The OCFG designed by this patent is stable and has at least one NE point.

[0129] The present invention designs an inter-layer link allocation algorithm based on OCFG, and the algorithm steps are as follows:

[0130] 1. Input: LEO satellite set U l

[0131] 2. Output: Stable LEO alliance division {U j l}

[0132] 3. Initialization: The satellites in the LEO satellite set are initialized into a non-overlapping alliance partition {U j l}, let the corresponding binary variable a ij (t) = 1

[0133] 4. Loop: segments from 1 to M;

[0134] 5. Randomly select a LEO satellite node and N i Includes Alliance Collection and does not include But the neighbor alliance that meets the service time condition

[0135] 6.IF N i <L m

[0136] 7. Calculate V c and V p =[V p1 ,V p2 ,V p3 ,…], and get the minimum mismatch value V p and the best alliance number

[0137] 8.IF V p <V c

[0138] 9. LEO Satellites Join the Alliance make p ij (t) = p i (t) / (N i +1)

[0139] 10. End IF

[0140] 11. End IF

[0141] 12. End the loop

[0142] The specific flow chart is as follows Figure 2 shown.

[0143] In order to demonstrate the performance advantages of the proposed method, the following simulation verification was performed. The simulation parameters are set as follows: the orbital altitudes of MEO satellites and LEO satellites are 12000km and 560km respectively, the orbital inclinations are both 70°, the number of orbits are 5 and 10 respectively, and the number of satellites in each orbit is 10 and 35 respectively. The bandwidth of the MEO intersatellite link is 40MHz, the transmission power is 12W, the bandwidth of the LEO intersatellite link is 20MHz, the transmission power is 5W, and the bandwidth of the interlayer link is 20MHz, the transmission power is 5W. The carrier frequency is 20GHz, the thermal noise is 354.81K, and the antenna gain is 36dBi. LEO satellites can access up to 5 MEO satellites, and MEO satellites can serve up to 65 LEO satellites.

[0144] Figure 3 The convergence of this method is simulated as the number of MEO satellites that LEO satellites can access simultaneously is L. m The changes in N m =8,N l =70. As can be seen from the figure, as the number of iterations increases, L m = 1, the mismatch remains unchanged. m As L increases, the convergence value of the OCFG inter-layer link A algorithm continues to decrease. This shows that the simultaneous unloading of traffic from LEO satellites to multiple MEO satellites effectively reduces the mismatch of satellites in the entire network. However, the convergence value does not increase with L m The increase has been decreasing, when L m =3,L m =4,L m = 5, the convergence values ​​of the algorithms are basically the same. This is due to the limitation of LEO satellite power. Sending data to too many MEO satellites at the same time reduces the transmission efficiency of LEO satellites, so the mismatch degree does not decrease all the time.

[0145] Figure 4 The figure shows the variation of mismatch degree with the number of LEO satellites under different access criteria, where N m =8. As can be seen from the figure, the random access criterion has the highest mismatch, followed by the most recent access criterion, the Pareto criterion and the selfish criterion are slightly smaller than the most recent access criterion, and the minimum mismatch of the proposed minimum mismatch criterion is always smaller than the comparison criterion. The mismatch of all strategies increases with the increase in the number of LEO satellites, but when L m =2 and L m =3, the mismatch rate of the proposed minimum mismatch criterion increases slower than that of other criteria. Figure 5 This shows that as the number of LEO satellites increases, the proposed method can effectively reduce the mismatch of satellites in the entire network.

[0146] Figure 5 The figure shows the variation of mismatch degree with the number of MEO satellites under different access criteria, where Nl =100. As can be seen from the figure, with the increase in the number of MEO satellites, the total network mismatch under the minimum mismatch criterion gradually decreases, and L m The larger the value, the smaller the mismatch. Among the comparison criteria, the mismatch of the random criterion increases with the increase of the number of MEO satellites. The mismatch of the nearest access criterion, the Pareto criterion and the selfish criterion are relatively close. Their mismatch first decreases with the increase of the number of MEO satellites. When the number of MEO satellites is 12, the mismatch increases slightly.

[0147] Example 2

[0148] This embodiment provides a multi-layer satellite network transmission demand offloading system, including:

[0149] Multiple LEO satellites are used to receive data packets from ground users through satellite-to-ground links, transmit data packets to the destination LEO satellite through LEO inter-satellite links, and establish inter-layer links with corresponding MEO satellites and unload excess transmission demands according to their own transmission capabilities and the size of transmission demands when the transmission demand exceeds their capabilities; each LEO satellite can independently select a MEO satellite to establish an inter-layer link, and this process is achieved by using a coalition formation game;

[0150] At least one MEO satellite is used to receive the transmission demand offloaded from the LEO satellite and perform the transmission.

[0151] The LEO satellite is also capable of receiving and forwarding data packets from neighboring satellites and sending to neighboring satellites with the same probability.

[0152] The LEO satellite transmits the data to be offloaded to the connected MEO satellite in an average manner.

[0153] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the technical principles of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A method for offloading transmission demand of a multi-layer satellite network, characterized in that: include: The LEO satellite receives data packets from ground users via satellite-to-ground links and transmits the data packets to the destination LEO satellite via LEO intersatellite links; When the transmission demand exceeds its capacity, the LEO satellite establishes an inter-layer link with the corresponding MEO satellite based on its own transmission capacity and the size of the transmission demand and unloads the excess transmission demand; Among them, each LEO satellite independently selects a MEO satellite to establish an inter-layer link, and the LEO satellite access to the MEO satellite problem is modeled as an overlapping coalition formation game; The problem of LEO satellite access to MEO satellite is modeled as an overlapping coalition formation game, including: Define the set of non-empty subsets of the set of LEO satellites that are considered to be overlapping federation structures; In an overlapping alliance structure, each LEO satellite is allowed to independently choose to join an alliance based on its strategy; Set the preference rule so that for any LEO satellite, the satellite has a tendency to leave the original alliance and join another alliance; For any LEO satellite LEO Satellites Prefer to leave the original alliance Join another alliance If and only if the following holds: Compared with the Alliance j1LEO satellite Prefer alliance j2, and represents the LEO satellites in the original alliance j2 and j1, Indicates LEO satellite Join the J2 Alliance, Indicates LEO satellite Leave alliance j1; Indicates the mismatch between the original J2 Alliance's transmission capabilities and transmission requirements. It indicates the mismatch between the transmission capacity and transmission demand of the original J1 alliance. Indicates LEO satellite The mismatch between the alliance's transmission capacity and transmission demand after joining J2. Indicates LEO satellite The mismatch between the alliance's transmission capacity and transmission demand after leaving J1; The judgment condition of alliance stability is established. When any LEO satellite cannot unilaterally change its alliance choice to improve its benefits according to the set preference rules, the alliance is judged to be in a stable state.

2. The multi-layer satellite network transmission demand unloading method according to claim 1, characterized in that: The LEO satellite is also capable of receiving and forwarding data packets from neighboring satellites and sending to neighboring satellites with the same probability.

3. The multi-layer satellite network transmission demand unloading method according to claim 1, characterized in that: The LEO satellite establishes an inter-layer link with the corresponding MEO satellite according to its own transmission capacity and transmission demand. The specific formula is as follows: Among them, the collection Includes MEO satellites in the alliance and LEO satellite collection represents the mismatch between the transmission capacity and transmission demand of alliance j, N m represents the number of MEO satellites, A is the inter-layer link matrix between LEO satellites and MEO satellites, and D k (t) and C k (t) represent the transmission demand and transmission capacity of satellite k at time t respectively.

4. The multi-layer satellite network transmission demand unloading method according to claim 1, characterized in that: In an overlapping alliance structure, each LEO satellite is allowed to independently choose to join an alliance based on its strategy. The specific formula is as follows: in, Indicates LEO satellite Forming a new alliance, p i (t) and N i are the transmission power of LEO satellites and the number of MEO satellites joining the alliance. The transmission power of LEO satellites is evenly distributed to each connected MEO satellite. ij (t) indicates LEO satellite With MEO satellite Inter-layer link transmit power.

5. The multi-layer satellite network transmission demand unloading method according to claim 1, characterized in that: LEO Satellites The utility function of is defined as: in, Indicates LEO satellite Access to MEO satellite The utility function when It indicates the mismatch between the transmission capacity and transmission demand of the original J1 alliance. Indicates LEO satellite The mismatch between the alliance's transmission capacity and transmission demand after leaving J1.

6. The multi-layer satellite network transmission demand unloading method according to claim 1, characterized in that: When any LEO satellite cannot unilaterally change its alliance selection to improve its benefits according to the set preference rules, the alliance is determined to be in a stable state, and the expression is as follows: in, and Represents LEO satellites The original alliance selection and the new alliance selection, Indicates LEO satellite In the original coalition's utility function, Indicates LEO satellite In the utility function of the new coalition, In addition to LEO satellites Alliance options for other LEO satellites.

7. A multi-layer satellite network transmission demand offloading system, characterized in that: include: Multiple LEO satellites are used to receive data packets from ground users through satellite-to-ground links, transmit data packets to the destination LEO satellite through LEO intersatellite links, and establish inter-layer links with corresponding MEO satellites and unload excess transmission demands according to their own transmission capabilities and the size of transmission demands when the transmission demand exceeds their capabilities; each LEO satellite can independently select a MEO satellite to establish an inter-layer link, and this process is achieved by using a coalition formation game; specifically, it includes: Define the set of non-empty subsets of the set of LEO satellites that are considered to be overlapping federation structures; In an overlapping alliance structure, each LEO satellite is allowed to independently choose to join an alliance based on its strategy; Set the preference rule so that for any LEO satellite, the satellite has a tendency to leave the original alliance and join another alliance; For any LEO satellite LEO Satellites Prefer to leave the original alliance Join another alliance If and only if the following holds: Compared with the Alliance j1LEO satellite Prefer alliance j2, and represents the LEO satellites in the original alliance j2 and j1, Indicates LEO satellite Join the J2 Alliance, Indicates LEO satellite Leave alliance j1; Indicates the mismatch between the original J2 Alliance's transmission capabilities and transmission requirements. It indicates the mismatch between the transmission capacity and transmission demand of the original J1 alliance. Indicates LEO satellite The mismatch between the alliance's transmission capacity and transmission demand after joining J2. Indicates LEO satellite The mismatch between the alliance's transmission capacity and transmission demand after leaving J1; Establish the criteria for determining alliance stability. When any LEO satellite cannot unilaterally change its alliance choice to improve its benefits according to the set preference rules, the alliance is considered to be stable. At least one MEO satellite is used to receive the transmission demand offloaded from the LEO satellite and perform the transmission.

8. The multi-layer satellite network transmission demand offloading system according to claim 7, characterized in that: The LEO satellite is also capable of receiving and forwarding data packets from neighboring satellites and sending to neighboring satellites with the same probability.

9. The multi-layer satellite network transmission demand offloading system according to claim 7, characterized in that: The LEO satellite transmits the data to be offloaded to the connected MEO satellite in an average manner.

Images