An Aircraft Internet Access Method Based on Inter-Satellite Links in an Integrated Space-Air-Ground Network

Abstract

An aircraft Internet access method based on inter-satellite links in an integrated space-air-ground network, which relates to an aircraft Internet access method. The present invention aims to solve the problem that existing space-air communication technologies ignore the satellite caching ability and the inter-satellite link ability. The steps of the present invention include Step 1, establishing an in-air Internet access architecture based on the integrated space-air-ground network and inter-satellite links; Step 2, the transmission process of an aircraft user's request for a file; Step 3, jointly optimizing the file download ratio and satellite connection to minimize the average delay of downloading files. The present invention belongs to the field of space-air communication technology.

Description

Technical Field

[0001] The present invention relates to an aircraft Internet access method, belonging to the technical field of aerospace communication. Background Art

[0002] In recent years, the demand for continuous and stable Internet connection has extended from ground networks to air flights. Passengers are eager to enjoy services such as watching movies, browsing websites, and sending text messages during flights. The latest report shows that 82% of respondents regard in-flight Internet access as a basic expectation of passengers. At the same time, it is reported that introducing in-flight WiFi will increase the average profit per passenger by 30 yuan, and may increase the income of airlines by hundreds of billions of yuan by 2035.

[0003] Due to the unique architecture of the sixth-generation communication network (6G), the space-air-ground integrated network makes reliable Internet access on aircraft a reality. When the files requested by passengers are not stored in the cabin, there are mainly two ways to obtain the files: The first method is through air-ground communication, that is, the aircraft directly connects to the ground gateway. Due to the short transmission distance, the latency of air-ground communication is usually low. However, it is difficult to deploy ground gateways in remote areas such as the ocean. In addition, the coverage area of ground gateways is much smaller than that of satellites. These two factors restrict the application of relying on ground gateways for in-flight Internet access. The second is through space-air communication, that is, the aircraft connects to the nearest visible satellite, and the satellite acts as a relay node between the ground and the aircraft. Although satellites can provide a wide coverage range, due to the long propagation distance, the transmission latency of the space-air communication Internet access method is higher than that of air-ground communication. For this reason, communication satellites with caching capabilities can share content between satellite networks through inter-satellite links and then directly send it to the aircraft, thus avoiding the forwarding process, so this method is more widely adopted.

[0004] The existing methods for aircraft Internet access through space-air communication mainly have the following defects: 1) The existing solutions ignore the caching capabilities of satellites, that is, it is assumed that all files are obtained from ground stations; during peak communication periods, the burden on ground stations is high, and the latency of the space-ground link will increase significantly; 2) The vast majority of existing solutions are in the form of single-hop relay between satellites and aircraft, while ignoring the capabilities of inter-satellite links.

[0005] Nowadays, by using laser communication technology, connections can be established between satellites, and a single-link transmission rate of up to 2.5 Gb / s can be provided. Compared with traditional radio frequency links, it can significantly reduce the transmission latency within the satellite network, thereby reducing the file acquisition latency of passengers. Summary of the Invention

[0006] In order to solve the problems that the existing space-air communication technology ignores the caching capabilities of satellites and the capabilities of inter-satellite links, the present invention further proposes an aircraft Internet access method based on inter-satellite links in a space-air-ground integrated network.

[0007] The technical solution adopted by the present invention to solve the above problems is as follows: The steps of the present invention include:

[0008] Step 1: Establish an in-air Internet access architecture based on the space-air-ground integrated network and inter-satellite links;

[0009] Step 2: The transmission process of file requests by aircraft users;

[0010] Step 3: Jointly optimize the file download ratio and satellite connection to minimize the average delay of downloaded files.

[0011] Further, the steps of establishing an in-air Internet access architecture based on the space-air-ground integrated network and inter-satellite links in Step 1 specifically include:

[0012] Step 101: Assume that in the space-air-ground integrated network, there are A civil aviation aircraft and S satellites running along their established routes. The movement of non-ground platforms at time t ∈ T, the set of civil aviation aircraft is represented as The satellites are represented as G gateways are deployed on the ground and connected to the core network through high-speed optical fiber links. Since the positions are fixed, it can be represented as G = {g1,..., g G};

[0013] Step 102: Assume that each gateway has all files, and each aircraft is connected to at most one satellite or ground gateway. The files are divided into cacheable content and non-cacheable content. The file set is F = {1,..., F}, and each file f ∈ F can be represented as (sn f , gt f , tp f , b f ), where sn f ∈ A is the source node aircraft that generates the file request, gt f ∈ T is the request generation time, tp f and b f are the file type and the number of data packets that make up the file respectively. Assume that the size of each data packet is R p bits;

[0014] Step 103: The space-air-ground network architecture includes four types of links:

[0015] The first type, the set of air-ground links, is represented as L G2A ;

[0016] The second type, the space-ground link L G2S ;

[0017] The third type, the air-space link L S2A ;

[0018] The fourth type, inter-satellite link L ISL ;

[0019] Step 104: Assume that the links in L G2A , L G2S and L S2A are all determined by the minimum distance. Assume that the frequency band resources used by each inter-satellite link are orthogonal, and use W ISL to represent its bandwidth. When satellite sends file f to satellite through inter-satellite link , the received signal-to-noise ratio of satellite is where P T (s k ) represents the transmission power of satellite s k , G T (s k ) and G R (s j ) represent the transmitting and receiving antenna gains respectively, L add-ISL is the additional path loss, and n0 is the noise power density;

[0020] Free space path loss depends on the transmission distance and can be expressed as where λ(s k , s j ) is the carrier wavelength. The achievable rate of inter-satellite link is

[0021] Step 105: Introduce the variable matrix where is a binary variable representing the satellite connection status. Define the file download ratio variable:

[0022] represents the ratio of satellite downloading file f from an external node. and belong to [0, 1]. The transmission rate of inter-satellite link is expressed as

[0023] Furthermore, the transmission process of the aircraft user requesting a file in Step 2 specifically includes:

[0024] Step 201: When can establish a connection with the ground gateway g m ∈G, the file request f can be directly transmitted through the air-ground link ; when cannot establish an air-ground link, where γ th is the minimum signal-to-noise ratio to ensure communication performance, and it will connect to the nearest satellite

[0025] Step 202, the satellite downloads the file from the node connected to it, which is called Stage 1; when the complete file is obtained, it will be integrated and sent to the aircraft which is called Stage 2

[0026] Furthermore, the process of Stage 1 is divided into two cases:

[0027] When the satellite cannot establish a connection with any ground gateway, it establishes a connection with other satellites through the inter-satellite link and obtains the file;

[0028] The satellite simultaneously obtains the file from the adjacent satellite and the ground gateway g m and obtains the file

[0029] Furthermore, the delay through the inter-satellite link in Stage 1 is:

[0030]

[0031] where represents the propagation delay;

[0032] The delay for downloading the file through the inter-satellite link is:

[0033]

[0034] where and respectively represent the sum of the propagation delay and the transmission delay of the space-ground link and the space-air link. The total delay for the aircraft to download the file f is:

[0035]

[0036] Furthermore, the optimization problem in Step 3 is:

[0037]

[0038] The steps to solve the above problem include:

[0039] Step 301, add the penalty function ò(S 2 - <π, v>) to the objective function. ε decreases according to π (l+1) = (l)×Δ update, where Δ is a constant and l is the number of iterations;

[0040] Step 302: Iteratively update π and v. The process is as follows: 1) Initialization: In the first iteration, l = 0, ò is a number close to 0, and set v (0) = 0;

[0041] 2) Optimize π given v. This sub-problem is a convex problem and can be directly solved;

[0042] 3) Optimize v given π: The closed-form solution to this problem is

[0043] 4) Repeat the above steps until convergence.

[0044] The beneficial effects of the present invention are as follows:

[0045] 1. The aircraft Internet access architecture and system provided by the present invention utilize the satellite caching ability to eliminate the relay forwarding of some files, thereby reducing the file transmission delay;

[0046] 2. In the file transmission method of the present invention, the powerful transmission ability of the inter-satellite links of the giant satellite constellation is utilized to solve the connection optimization problem of multiple inter-satellite links, further enhancing the Internet access experience of aircraft users through space-air-ground communication. BRIEF DESCRIPTION OF THE DRAWINGS

[0047] Figure 1 is a schematic diagram of aircraft Internet access based on inter-satellite links in a space-air-ground integrated network;

[0048] Figure 2 is the flowchart of the proposed in-air Internet access architecture;

[0049] Figure 3 is a schematic diagram of the variation of the average delay with the number of file requests per time slot;

[0050] Figure 4 is a schematic diagram of the relationship between the average delay and the maximum number of inter-satellite links. DETAILED DESCRIPTION OF THE INVENTION

[0051] DETAILED DESCRIPTION OF THE INVENTION I: In combination with Figures 1 to 4 This embodiment is described. The method for aircraft Internet access based on inter-satellite links in a space-air-ground integrated network according to this embodiment is implemented through the following steps:

[0052] Step 1: Establish an in-air Internet access architecture based on a space-air-ground integrated network and inter-satellite links;

[0053] Step 2: The transmission process of file requests by aircraft users;

[0054] Step 3: Jointly optimize the file download ratio and satellite connections to minimize the average delay of downloaded files.

[0055] Specific Embodiment 2: In combination with Figures 1 to 4 To illustrate this embodiment, in step 1 of the method for an aircraft to access the Internet based on an inter-satellite link in an air-space-ground integrated network, the steps of establishing an air-based Internet access architecture based on the air-space-ground integrated network and the inter-satellite link specifically include:

[0056] Step 101. Assume that in the air-space-ground integrated network, there are A civil aviation aircraft and S satellites running along their established routes. The movement of non-ground platforms at time t ∈ T, the set of civil aviation aircraft is represented as The satellites are represented as G gateways are deployed on the ground and connected to the core network through high-speed optical fiber links. Since their positions are fixed, they can be represented as G = {g1,..., g G};

[0057] Step 102. Assume that each gateway has all files, and each aircraft is connected to at most one satellite or ground gateway. The files are divided into cacheable content and non-cacheable content. The file set is F = {1,..., F}, and each file f ∈ F can be represented as (sn f , gt f , tp f , b f ), where sn f ∈ A is the source node aircraft that generates the file request, gt f ∈ T is the request generation time, tp f and b f are the file type and the number of data packets that make up the file respectively. Assume that the size of each data packet is R p bits;

[0058] Step 103. The air-space-ground network architecture includes four types of links:

[0059] The first type, the set of air-ground links, is represented as L G2A ;

[0060] The second type, the space-ground link L G2S ;

[0061] The third type, the air-space link L S2A ;

[0062] The fourth type, the inter-satellite link L ISL ;

[0063] Step 104. Assume that the links in L G2A , L G2S and L S2A are all determined by the minimum distance. Assume that the frequency band resources used by each inter-satellite link are orthogonal, and use W ISLdenotes its bandwidth. When the satellite sends the file f to the satellite through the inter-satellite link , the received signal-to-noise ratio of the satellite is where P T (s k ) represents the transmission power of satellite s k , G T (s k ) and G R (s j ) represent the transmitting and receiving antenna gains respectively, L add-ISL is the additional path loss, and n0 is the noise power density;

[0064] Free space path loss depends on the transmission distance and can be expressed as where λ(s k , s j ) is the carrier wavelength. The achievable rate of the inter-satellite link is

[0065] Step 105: Introduce the variable matrix where is a binary variable representing the satellite connection status. Define the file download ratio variable:

[0066] represents the ratio of satellite downloading file f from an external node. and belong to [0, 1]. The transmission rate of the inter-satellite link is expressed as

[0067] Specific Embodiment 3: Combine Figures 1 to 4 to illustrate this embodiment. In Step 2 of the method for an aircraft to access the Internet based on an inter-satellite link in a space-air-ground integrated network described in this embodiment, the transmission process of the aircraft user's file request specifically includes:

[0068] Step 201: When can establish a connection with the ground gateway g m ∈G, the file request f can be directly transmitted through the space-ground link ; when cannot establish a space-ground link, where γ th is the minimum signal-to-noise ratio to ensure communication performance, and it will connect to the nearest satellite

[0069] Step 202: The satellite Downloading a file from the nodes connected to it is called Phase 1; when After obtaining the complete file, it will be integrated and sent to the aircraft which is called Phase 2.

[0070] Embodiment 4: In combination with Figures 1 to 4 To illustrate this embodiment, the process of Phase 1 of the method for an aircraft to access the Internet based on inter-satellite links in an air-space-ground integrated network described in this embodiment is divided into two cases:

[0071] When the satellite cannot establish a connection with any ground gateway, it establishes a connection with other satellites through inter-satellite links and obtains the file;

[0072] The satellite simultaneously obtains files from adjacent satellites and the ground gateway g m .

[0073] Embodiment 5: In combination with Figures 1 to 4 To illustrate this embodiment, the delay through the inter-satellite link in Phase 1 of the method for an aircraft to access the Internet based on inter-satellite links in an air-space-ground integrated network described in this embodiment is:

[0074]

[0075] where represents the propagation delay;

[0076] The delay for downloading a file through the inter-satellite link is:

[0077]

[0078] where and respectively represent the sum of the propagation delay and the transmission delay of the space-ground link and the air-space link. The total delay for the aircraft to download the file f is:

[0079]

[0080] Embodiment 6: In combination with Figures 1 to 4 To illustrate this embodiment, the optimization problem in Step 3 of the method for an aircraft to access the Internet based on inter-satellite links in an air-space-ground integrated network described in this embodiment is:

[0081]

[0082] The steps to solve the above problem include:

[0083] Step 301. Add a penalty function ò(S 2 -<π,v>) to the objective function. ε is updated according to π (l+1) = (l) ×Δ in each iteration, where Δ is a constant and l is the iteration number;

[0084] Step 302. Iteratively update π and v. The process is as follows: 1) Initialization: In the first iteration, l = 0, ò is a number close to 0, and set v (0) = 0;

[0085] 2) Optimize π given v. This sub-problem is a convex problem and can be directly solved;

[0086] 3) Optimize v given π: The closed-form solution of this problem is

[0087] 4) Repeat the above steps until convergence.

[0088] In this embodiment, to solve problem P1, the following lemma is first given:

[0089] Lemma 1: 1) The optimal solution should satisfy that the transmission delay of each link is consistent; 2) The satellite should establish as many inter-satellite links as possible to minimize the delay.

[0090] According to Lemma 1, for any s that satisfies j , s k , the transmission delay of each inter-satellite link is

[0091] Thus, the continuous variables are eliminated, and problem P1 can be transformed into the following problem, leaving only discrete binary variables:

[0092]

[0093] Since the dimension of the above problem is large, traditional methods such as the exhaustive method face the problem of high complexity. Therefore, an exact penalty function method is proposed to solve it. First, the following theorem is given:

[0094] Theorem 1: Define and If (u, v) ∈ Θ, then u ∈ {-1, 1} m×n , v ∈ {-1, 1} m×n and u = v.

[0095] According to Theorem 1, and introducing π f (s k , s j ) = 2x f (s k , s j ​) - 1, binary constraint x f (s k , s j ) ∈ {0, 1} is equivalent to Problem P2 is equivalent to

[0096]

[0097] Simulation and Results

[0098] Assume that the whole day is evenly divided into consecutive time slots of 15 s. 120 satellites in the system are distributed on 6 orbital planes at an altitude of 1000 km, with an orbital inclination of 53°. The Airbus A320 aircraft generates at most one service request in each time slot. Passengers have four types of file requests: music, images, videos, and instant messages. The number of packets constituting the file is uniformly distributed in the ranges of [50, 100], [500, 1000], [1000, 3000], and [10, 1000], with 1080 bits per packet. The default number of inter-satellite links and base stations are 2 and 5 respectively. The carrier frequencies of the space-air, air-ground, and ground-air links are 15 GHz, 18 GHz, and 30 GHz respectively, and the bandwidths are all 100 MHz. The antenna gains of the satellites, aircraft, and base stations are 40 dB, 30 dB, and 52 dB respectively. The transmission powers of the satellites and base stations are 5 W and 10 W respectively. The frequency, bandwidth, and antenna gain of the inter-satellite laser link are 197 THz, 50 MHz, and 90 dB. The additional path losses of the space-air links are 5.2 dB and 2.5 dB respectively. Select the following benchmark algorithms: 1) Randomly select satellite connection relationships. 2) Exhaustive search to obtain the lower bound of the delay. 3) Greedy algorithm, that is, each satellite selects the link with the largest capacity to establish a connection.

[0099] From Figure 3 It can be seen that according to our algorithm, the average download delay of the file is close to that of the exhaustive search, and at the same time is much smaller than that of the greedy algorithm and the random algorithm, which confirms the effectiveness of the proposed algorithm. In addition, when the file requests are few, the greedy algorithm can also achieve good performance, because the requests are sparse, so selecting the link with the largest capacity is usually the optimal solution. From Figure 4 It can be seen that increasing the maximum allowed number of inter-satellite links can significantly reduce the delay, because the laser link can provide a very high transmission rate, so it can be foreseen that the proposed in-air Internet access method is more applicable under the future development trend of inter-satellite links.

[0100] The above are only the preferred embodiments of the present invention, and do not impose any form of limitation on the present invention. Although the present invention has been disclosed above with the preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make some changes or modifications to equivalent embodiments by using the above-disclosed technical content within the scope of the technical solution of the present invention. However, as long as it does not depart from the content of the technical solution of the present invention and is based on the technical essence of the present invention, any simple modification, equivalent replacement, and improvement made to the above embodiments still fall within the protection scope of the technical solution of the present invention.

Claims

1. A method for an aircraft to access the Internet based on inter-satellite links in an integrated space-air-ground network, characterized in that: The method for an aircraft to access the Internet based on inter-satellite links in an integrated space-air-ground network is implemented through the following steps: Step 1: Establish an in-air Internet access architecture based on the integrated space-air-ground network and inter-satellite links; Step 2: The transmission process of file requests from aircraft users; Step 3: Jointly optimize the file download ratio and satellite connections to minimize the average delay of downloaded files; The optimization problem is: The steps to solve the above problem include: Step 301: Add a penalty function to the objective function , , Update in each iteration according to , where is a constant is the number of iterations; Step 302, iterative update and , the process is as follows: 1) Initialization: In the first iteration, , is a number close to 0, set ; 2) Given optimization , this sub-problem is a convex problem and can be directly solved; 3) Given optimize : The closed-form solution to this problem is ; 4) Repeat the above steps until convergence; To solve the problem , the following lemma is given first: Lemma 1: 1) The optimal solution should satisfy that the transmission delays of each link are consistent; According to Lemma 1, for any that satisfies , the transmission delay of each inter-satellite link is Thus, the continuous variables are eliminated, and the problem is transformed into the following problem, with only discrete binary variables remaining: Propose a method of exact penalty function to solve; First, give the following theorem: Theorem 1: Definition , and ; If , then there is , and ; According to Theorem 1 and introducing , the binary constraint is equivalent to problem is equivalent to 。 2. The method for an aircraft to access the Internet based on an inter-satellite link in a space-air-ground integrated network according to claim 1, wherein: The steps of establishing an in-air Internet access architecture based on the integrated space-air-ground network and inter-satellite links in Step 1 specifically include: Step 101. Assume that in the integrated air, space and ground network, there are civil aviation aircraft and satellites operating along their established routes. The movement of non-ground platforms at time . The set of civil aviation aircraft is represented as , and the satellites are represented as . gateways are deployed on the ground and connected to the core network through high-speed optical fiber links. Since their positions are fixed, they are represented as ; Step 102. Assume that each gateway has all the files, and each aircraft is connected to at most one satellite or ground gateway. The files are divided into cacheable content and non-cacheable content, and the file set is , and each file is represented as , where is the source node aircraft that generates the file request, is the request generation time, and are the file type and the number of data packets that make up the file respectively. Assume that the size of each data packet is bits; Step 103: The integrated space-air-ground network architecture includes four types of links: The first type, the air-ground link set, is denoted as ; Second, space-earth link ; The third type: space-air link ; The fourth type: Inter-satellite link ; Step 104. Assume that , and the links in are all determined by the minimum distance. Assume that the frequency band resources adopted by each inter-satellite link are orthogonal, and use to represent its bandwidth. When satellite sends a file to satellite through the inter-satellite link , the received signal-to-noise ratio of satellite is , where represents the transmission power of satellite , and represent the antenna gains of the transmitter and receiver respectively, is the additional path loss, is the noise power density; Free space path loss Depends on the transmission distance , expressed as , where is the carrier wavelength, and the achievable rate of the inter-satellite link is ; Step 105, introduce a variable matrix , where is a binary variable representing the satellite connection status, and define a file download ratio variable: , representing the satellite Download files from external nodes Ratio of and Belong to , inter-satellite link The transmission rate of is expressed as .

3. The method for an aircraft to access the Internet based on an inter-satellite link in a space-air-ground integrated network according to claim 1, wherein: The transmission process of file requests from aircraft users in Step 2 specifically includes: Step 201, when establishes a connection with the ground gateway the file request is directly transmitted via the air-ground link ; when the air-ground link cannot be established, , where is the minimum signal-to-noise ratio to ensure communication performance, and it will connect to the nearest satellite ; Step 202, Satellite Downloads a file from a node connected thereto, referred to as Phase 1; when After obtaining the complete file, it will be integrated and sent to the aircraft , referred to as Phase 2.

4. The method for an aircraft to access the Internet based on an inter-satellite link in a space-air-ground integrated network according to claim 3, wherein: The process of Phase 1 is divided into two cases: When the satellite is unable to establish a connection with any ground gateway, it uses an inter-satellite link to establish a connection with other satellites and obtain files; Satellite Simultaneously obtain files from adjacent satellites and the ground gateway ​ 5. The method for an aircraft to access the Internet based on an inter-satellite link in an integrated space-air-ground network according to claim 3, wherein: The delay through the inter-satellite link in Phase 1 is: wherein represents the propagation delay; The delay of downloading files through the inter-satellite link is: where and represent the sum of the propagation delay and the transmission delay of the terrestrial link and the space-air link respectively. The total delay for the aircraft to download a file is as follows: 。

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