Low earth orbit satellite switching method based on double activation protocol stacks

Abstract

The invention relates to a low-orbit satellite switching method based on a double-activation protocol stack, and belongs to the technical field of satellite mobile communication. The method comprises the following steps: establishing a non-ground network in a low earth orbit satellite network environment, designing a dual-activation protocol stack-based switching architecture taking maximization of the average rate of user equipment and minimization of switching interruption delay as optimization objectives, and establishing an original optimization problem; establishing a low earth orbit satellite network multi-stage switching mechanism; decomposing an original optimization problem into a bandwidth allocation sub-problem and a switching strategy sub-problem based on the established multi-stage switching mechanism; solving the bandwidth allocation sub-problem by adopting an alternating direction multiplier method; solving the switching strategy sub-problem by adopting a simulation degradation algorithm; and combining solving results of the bandwidth allocation sub-problem and the switching strategy sub-problem to obtain a final optimal solution. According to the invention, challenges caused by frequent satellite switching and limited satellite resources in the satellite network can be effectively handled, high-speed and seamless connection is realized, and the user experience is improved.

Description

Technical Field

[0001] The invention belongs to the technical field of satellite mobile communications and relates to a low-orbit satellite switching method based on a dual-activation protocol stack. Background Art

[0002] As a powerful supplement to wireless and fixed terrestrial communications, non-terrestrial networks (NTNs) have become an important part of the 5G era and the upcoming 6G era, providing ubiquitous connectivity for various devices and applications. Compared with traditional high-orbit and medium-orbit satellite constellation systems, emerging satellite networks are mainly composed of low-Earth orbit (LEO) satellites. LEO satellite constellations have significant advantages, including seamless service coverage and significantly reduced latency. 3GPP began to explore the possibility of using satellites and aerial platforms to provide network connectivity for user equipment (UE) in Release 15, and further advanced this work in Release 16, especially by studying how to adapt 5G New Radio (NR) to support non-terrestrial networks (NTN).

[0003] Unlike the fixed base stations of terrestrial networks, the low orbit altitude of LEO satellites (usually between 500 km and 1200 km) provides lower transmission delays and enhanced wireless link budgets. However, these advantages also bring challenges, especially the highly dynamic connection between satellites and users, which leads to frequent switching during user services. In order to ensure the stability of network connections and the continuity of services, mobility management, especially switching management, is particularly important. Mobility enhancement support is an important challenge in 5G mobile communication systems. The ultimate goal of 5G networks is to achieve near-zero mobility interruption time (MIT), that is, the shortest time during which the user equipment (UE) supported by the system cannot exchange user plane data packets with any base station (BS) during the handover process. MIT is defined as the sum of the recovery time in handover failure (HOF) and the handover interruption time (HIT) in successful handover (HO).

[0004] In recent years, 3GPP has proposed a variety of 5G network mobility enhancement technologies aimed at minimizing MIT and improving handover efficiency. During the handover (HO) process based on the dual activation protocol stack (DAPS), the user equipment (UE) maintains a connection with both the source base station and the target base station. To support this handover, the UE must activate dual protocol stacks: one user plane protocol stack for the target cell, including the physical layer (PHY), the media access control layer (MAC), and the radio link control layer (RLC); and the other user plane protocol stack for transmitting and receiving user data in the source cell.

[0005] However, existing ground-based mobility enhancement technologies are not applicable to low-orbit satellite networks because satellite resources are limited and network topology is highly dynamic. This makes satellite networks with limited service quality even more unstable. Therefore, these research methods are difficult to effectively adapt to LEO satellite communication scenarios. Research on switching methods in satellite networks urgently needs to ensure that service quality is guaranteed while considering network dynamics. Summary of the invention

[0006] In view of this, an object of the present invention is to provide a low-orbit satellite switching method based on a dual-activation protocol stack.

[0007] In order to achieve the above object, the present invention provides the following technical solutions:

[0008] A low-orbit satellite switching method based on a dual-activation protocol stack, the method comprising the following steps:

[0009] S1. Establish a non-terrestrial network in a low-orbit satellite network environment, design a switching architecture based on a dual-active protocol stack with the optimization objectives of maximizing the average rate of user equipment and minimizing the switching interruption delay, and establish the original optimization problem;

[0010] S2. Establish a multi-stage handover mechanism for the low-orbit satellite network, which at least includes a state acquisition stage, a target satellite selection stage, a handover execution stage, and a data transmission stage;

[0011] S3, based on the established multi-stage switching mechanism, the original optimization problem is decomposed into a bandwidth allocation sub-problem and a switching strategy sub-problem;

[0012] S4, using the alternating direction multiplier method to solve the bandwidth allocation subproblem;

[0013] S5. Using simulated degradation algorithm to solve the switching strategy sub-problem;

[0014] S6. Combine the solution results of the bandwidth allocation subproblem and the switching strategy subproblem to obtain the final optimal solution.

[0015] Further, in step S1, the established non-terrestrial network includes N satellites and K users, and a time frame structure is designed, where the length of each frame is Δt, and the switching interruption delay is t ho ;

[0016] Adopt a collection Represents the N satellites in the satellite constellation, the set represents the set of all users, and the users are randomly distributed within the coverage of N satellites. The user set is divided into users supporting the switching strategy based on the dual-activation protocol stack and users using the traditional switching strategy. The user set supporting the dual-activation protocol stack is

[0017] Design correlation index xk,n t Describe user u k With satellite S n During the switching process, the connection status When the satellite S n Is user u k The service satellite of the target satellite S m set up To capture the associated transfer status after the switch is completed;

[0018] use Represents the switching strategy, and its value is [-1,0,1], where Represents user u k Use the dual-activation switching strategy to switch to the target satellite S n ; Indicates that the user maintains the current connection status and does not switch; Represents user u k Use the traditional switching strategy to switch to the target satellite S n , interruption delay is allowed;

[0019] Assume that at time t, satellite S n For user u k The allocated bandwidth is It satisfies the following bandwidth allocation constraints:

[0020]

[0021] In the formula, B n is the maximum bandwidth of each satellite;

[0022] A channel model between the satellite and the user is established, which includes path loss and Rayleigh fading. The path loss is calculated as:

[0023]

[0024] Where c is the speed of light, is the distance between UE and satellite, f is the carrier frequency;

[0025] Channel Vector represents the channel response from the satellite to the UE, which follows Rayleigh fading and is a circularly symmetric complex Gaussian random variable with zero mean and unit variance.

[0026] Under Rayleigh fading conditions, the signal-to-noise ratio (SNR) and channel gain are Related, the calculation formula of SNR is:

[0027]

[0028] Where P A represents the satellite's transmission power, and N0 is the noise power;

[0029] Then we have:

[0030]

[0031] In the formula, For user u k At time t from satellite S n Received downlink rate.

[0032] Further, in the established handover architecture based on the dual-activation protocol stack, the handover strategy based on the dual-activation protocol stack allows the user equipment UE to maintain a downlink connection with two satellites at the same time during the handover execution phase, during which the source satellite continues to allocate the downlink packet data convergence protocol layer sequence number SN until the allocation task is formally handed over to the target satellite;

[0033] The target satellite receives and retransmits all downlink data forwarded by the source satellite through the Xn interface, prioritizes all downlink data, and then forwards the downlink PDCP SDU that does not contain the sequence number SN;

[0034] In the handover execution phase, the downlink data received by the user includes the superimposed data of the source and target satellites, as well as the protocol processing data;

[0035] Among them, the amount of data received by the target satellite is expressed as:

[0036]

[0037] Where α is the implementation loss factor, which is used to adjust the difference between the theoretical maximum data rate and the actual implementation rate; Indicates satellite S m Load; represents the number of users switched to the target satellite; t interval is the data request interval, t off The data request lead time offset is used to request data in advance;

[0038] Assume that the amount of data sent by the source satellite is expressed as:

[0039]

[0040] Target satellite S m The amount of data sent is:

[0041]

[0042] Where, t hoIndicates the duration of the phase;

[0043] Then, the total amount of data received by the user is expressed as:

[0044]

[0045] Calculate the ratio of packets:

[0046]

[0047] Calculate u k The effective amount of data:

[0048]

[0049] The downlink rate of the user during the handover execution phase is expressed as:

[0050]

[0051] Introducing an additional delay T DAPS Reorder the received data packets with a reordering delay T DAPS There is an upper bound, which is defined as the source satellite S n and the target satellite S m The maximum difference between nodes’ expected downstream delays is expressed as:

[0052] T DAPS ≤|E[T S-Sat ]-E[T T-Sat ]|

[0053] Among them, E[T S-Sat ] represents the source satellite S n The expected downlink delay is Represents user u k With satellite S n Downlink outage probability, Represents user u k With satellite S n Downlink transmission delay, Represents user u k With satellite S n The downlink transmission delay of the target satellite takes into account the inter-satellite link delay T Xn , the expected downlink delay of the target satellite E[T T-Sat ] is expressed as:

[0054]

[0055] Represents user u k With satellite Sm Downlink outage probability, Represents user u k With satellite S m Downlink transmission delay, Represents user u k With satellite S m Downlink transmission delay for retransmission via the HARQ entity;

[0056] Connection interruption probability P out It is defined as the signal-to-noise ratio of the user equipment in the satellite-user transmission is lower than the predetermined threshold γ th The probability of is expressed as:

[0057]

[0058] Define a new variable:

[0059]

[0060] Then X~Exp(Y k ),in The connection interruption probability is further expressed as:

[0061]

[0062] Downlink delay T 1 Mainly determined by the propagation delay, under the hybrid automatic repeat request mechanism, if a data packet is retransmitted once, the downlink delay T 2 Expressed as Where c represents the speed of light;

[0063] The downlink delay of DAPS switching is lower than that of the traditional switching strategy, satisfying the following inequality:

[0064] maxT DAPS ≤T HIT

[0065] Right now:

[0066]

[0067] Among them, T HIT is the downlink delay of the traditional switching strategy.

[0068] Further, according to the established switching architecture based on the dual-active protocol stack, the original optimization problem P1 established with maximizing the average rate of the user equipment and minimizing the switching interruption delay as the optimization goal is expressed as:

[0069]

[0070] Among them, C1.1 indicates the user of the integrated dual-activation protocol stack switching strategy, while the rest of the users use the traditional switching strategy; C1.2 stipulates that the bandwidth allocation of the service users meets the minimum guarantee requirements; C1.3 and C1.4 specify that each user can only switch to one target satellite at the same time, and the source satellite and the target satellite are different; C1.5 ensures that the total bandwidth allocated to each satellite does not exceed its available bandwidth limit; C1.6 and C1.7 define the conditions for the use of the dual-activation switching strategy, among which C1.6 ensures that the target satellite can handle data loads exceeding a predetermined threshold, and C1.7 sets an upper limit for the packet reordering delay at the PDCP layer.

[0071] Furthermore, in step S2, in the established low-orbit satellite network multi-stage switching mechanism, within a single time frame, the satellite topology remains stable, the length of each time frame is fixed to Δt, and each time frame is divided into the following four stages:

[0072] Status acquisition phase: Each satellite measures the signal strength of its service users and exchanges relevant signal information with neighboring satellites to obtain the global network status;

[0073] Target satellite selection phase: Each satellite independently determines the best target satellite for the next hop handover based on local status information;

[0074] Handover execution phase: According to the handover decision, the user equipment UE establishes a downlink connection with the target satellite. The duration of this phase is t ho , used to complete the switching execution and the exchange of related protocols;

[0075] Data transmission phase: During this phase, each source satellite continuously transmits data to its service users. This phase will last until the next status acquisition phase begins;

[0076] If within a time frame, satellite S n According to the measurement results of the target satellite selection phase, the user u k If no handover is required, the handover execution phase will not be initiated and the user's downlink data transmission will continue to be provided by the satellite.

[0077] Further, in step S3, first Relaxation is a continuous variable with a range of [-1,1]; secondly, a new variable is introduced and represents the positive and negative parts of the slack variable; finally, the optimization problem is restructured and decomposed into the bandwidth allocation problem and the switching strategy problem; among them,

[0078] The slack variable is the time required for the user to connect to the target satellite after executing the switching decision. The original optimization problem P1 is optimized to P2:

[0079]

[0080] By fixing the switching strategy variables and bandwidth allocation variables respectively, the original problem is decomposed into two independent sub-problems for solution, where the objective function value J * (ξ) is defined as -∞, and only b is taken as a free variable, and the bandwidth allocation subproblem is obtained:

[0081]

[0082] stC2.3,C2.6,C2.7

[0083] Then, based on the solution of the bandwidth allocation subproblem, the switching strategy subproblem is further obtained:

[0084]

[0085] stC2.1,C2.2,C2.4~C2.8

[0086] Where ξ is the independent variable of the switching strategy subproblem.

[0087] Further, in step S4, the bandwidth allocation sub-problem is solved in the switching strategy In the fixed case, it is a convex optimization problem. A distributed algorithm based on the alternating direction multiplier method is used to decompose the problem into multiple subproblems, each of which involves only one satellite, and the global optimization problem is solved by coordinating local variables.

[0088] Further, in step S5, the switching strategy optimization sub-problem is solved by using a simulated annealing algorithm, by iteratively adjusting the switching strategy and accepting non-optimal solutions according to a preset probability to avoid falling into a local optimum, and finally finding a global optimal solution;

[0089] In each iteration, the simulated annealing algorithm randomly selects a neighborhood solution of the current strategy and calculates the objective function value corresponding to the solution. If the objective function value of the neighborhood solution is better than the current solution, the solution is directly accepted; otherwise, the non-optimal solution is accepted based on the control probability of the current temperature. As the algorithm iterates, the temperature gradually decreases, reducing the probability of accepting non-optimal solutions, thereby exploring the optimal switching strategy from a global perspective.

[0090] Further, in step S6, by solving the bandwidth allocation and switching strategy optimization sub-problems respectively, a final optimization solution is obtained so as to maximize the average rate of the UE and minimize the switching interruption time;

[0091] In each time frame, the system solves the bandwidth allocation and switching strategy optimization sub-problems respectively. The solution of each sub-problem is carried out independently, and a coordination and feedback mechanism is established between the two. The bandwidth allocation optimization dynamically adjusts the resource allocation by considering the bandwidth resources and user needs of each satellite, while the switching strategy optimization adjusts the switching decision to minimize the interruption time according to the current network status and user location.

[0092] Further, in step S6, a greedy reduction method is used to reduce the slack variable ξ according to the solution of the bandwidth allocation and switching strategy optimization problem, and the process is as follows:

[0093] First, determine the size of ξ. When the value of ξ is not equal to 0, if it is greater than 0, it is set to 1; if it is less than 0, it is set to -1;

[0094] The restored ξ value is then brought back to the constraint conditions for verification. If the constraint conditions are met, the restoration process is completed; otherwise, the above operations are continued until a switching strategy ξ that meets the constraint requirements is finally obtained.

[0095] The beneficial effects of the present invention are:

[0096] The present invention takes into full consideration the high dynamics and resource allocation issues in the low-orbit satellite network (LEO), and proposes a switching method based on the dual-activation protocol stack (DAPS). This method maintains the connection between the user equipment (UE) and the source base station and the target base station at the same time during the switching process, and adopts a distributed optimization strategy, which effectively guarantees the user's high downlink rate while ensuring low switching interruption delay.

[0097] Other advantages, objectives and features of the present invention will be described in the following description to some extent, and to some extent, will be obvious to those skilled in the art based on the following examination and study, or can be taught from the practice of the present invention. The objectives and other advantages of the present invention can be realized and obtained through the following description. BRIEF DESCRIPTION OF THE DRAWINGS

[0098] In order to make the purpose, technical solutions and advantages of the present invention more clear, the present invention will be described in detail below in conjunction with the accompanying drawings, wherein:

[0099] Figure 1 It is an overall flow chart of the low-orbit satellite switching method based on the dual-activation protocol stack of the present invention;

[0100] Figure 2 A schematic diagram of performing dual-active stack switching in a satellite network according to the present invention. DETAILED DESCRIPTION

[0101] The following describes the embodiments of the present invention by specific examples, and those skilled in the art can easily understand other advantages and effects of the present invention from the contents disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and the details in this specification can also be modified or changed in various ways based on different viewpoints and applications without departing from the spirit of the present invention. It should be noted that the illustrations provided in the following embodiments only illustrate the basic concept of the present invention in a schematic manner, and the following embodiments and features in the embodiments can be combined with each other without conflict.

[0102] Among them, the drawings are only used for illustrative explanations, and they only represent schematic diagrams rather than actual pictures, and should not be understood as limitations on the present invention. In order to better illustrate the embodiments of the present invention, some parts of the drawings may be omitted, enlarged or reduced, and do not represent the size of actual products. For those skilled in the art, it is understandable that some well-known structures and their descriptions in the drawings may be omitted.

[0103] The same or similar numbers in the drawings of the embodiments of the present invention correspond to the same or similar parts; in the description of the present invention, it should be understood that if the terms "upper", "lower", "left", "right", "front", "rear", etc. indicate the orientation or position relationship, they are based on the orientation or position relationship shown in the drawings, which is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operate in a specific orientation. Therefore, the terms describing the position relationship in the drawings are only used for illustrative purposes and cannot be understood as limiting the present invention. For ordinary technicians in this field, the specific meanings of the above terms can be understood according to specific circumstances.

[0104] See also Figure 1-2 , which is a low-orbit satellite switching method based on a dual-activation protocol stack.

[0105] Example

[0106] This embodiment provides a detailed implementation step of a low-orbit satellite switching method based on a dual-activation protocol stack, such as Figure 1 As shown, it includes the following steps:

[0107] S1. In a low-orbit satellite network environment, a switching architecture based on a dual-active protocol stack (DAPS) is designed to optimize network throughput and minimize switching interruption delay. The architecture comprehensively considers key factors such as switching interruption time and user rate, and constructs an original optimization model to maximize the average rate of user equipment (UE);

[0108] Non-terrestrial networks (NTNs) consist of N satellites and K users. A time frame structure is proposed, where the length of each frame is Δt, and the switching interruption delay is tho .gather Represents the N satellites in the satellite constellation, the set represents the set of all users, and the users are randomly distributed within the coverage of N satellites. The set of users supporting the Dual Activation Protocol Stack (DAPS) is The remaining users adopt the traditional switching strategy, allowing a certain switching interruption delay.

[0109] In each coverage interval, since each user may be covered by multiple satellites, the association index xk,n in the dual activation protocol stack (DAPS) switching is t Used to describe user u k With satellite S n The connection status during the switching process. When the satellite S n Is user u k There is a downlink between the target satellite S m set up The associated transfer status after the switch is completed can be accurately captured.

[0110] make Represents the switching strategy, and its value range is [-1,0,1], where Represents user u k Use the dual-activation switching strategy to switch to the target satellite S n , Indicates that the user maintains the current connection status and does not switch. Represents user u k Use the traditional switching strategy to switch to the target satellite S n , allowing a certain interrupt delay.

[0111] use Denotes the satellite S at time t n For user u k The allocated bandwidth. Since the bandwidth of each satellite is limited, its maximum bandwidth is recorded as B n , so we can get the following bandwidth allocation constraints:

[0112]

[0113] The channel model between the satellite and the UE includes path loss and Rayleigh fading. The path loss is calculated by the following formula:

[0114]

[0115] Where c is the speed of light, is the distance between the UE and the satellite, and f is the carrier frequency. In this embodiment, the path loss The unit is dB, distance The unit of is km, and the unit of carrier frequency f is MHZ.

[0116] Channel Vector represents the channel response from the satellite to the UE, which follows Rayleigh fading and is a circularly symmetric complex Gaussian random variable with zero mean and unit variance.

[0117] Under Rayleigh fading conditions, the signal-to-noise ratio (SNR) and channel gain are Related, the calculation formula of SNR is:

[0118]

[0119] Where P A represents the satellite's transmission power, and N0 is the noise power. Based on the above model, user u k At time t from satellite S n The received downlink rate calculation formula is:

[0120]

[0121] Unlike traditional handover strategies in wireless networks, the handover strategy based on the dual-activation protocol stack allows the user equipment (UE) to maintain a downlink connection with both satellites during the handover execution phase. During this phase, the source satellite continues to allocate downlink packet data convergence protocol (PDCP) layer sequence numbers (SNs) until the allocation task is officially handed over to the target satellite. In addition, the target satellite receives and retransmits all downlink data forwarded by the source satellite through the Xn interface, prioritizes the data, and then forwards the downlink PDCP SDU that does not contain the sequence number (SN). During the handover execution phase, the downlink data received by the user not only simply superimposes the data of the two satellites, but also includes complex protocol processing.

[0122] The amount of data received by the target satellite can be expressed as:

[0123]

[0124] Where α is the implementation loss factor (usually set to 0.6), which is used to adjust the difference between the theoretical maximum data rate and the actual implementation rate; Indicates satellite S m Load; represents the number of users switched to the target satellite; t interval is the data request interval, t off The data request lead time offset is used to request data in advance.

[0125] For research user u kUnder the dual-activation protocol stack switching strategy, there are two downlink rate issues during the switching execution phase. First, assume that the amount of data sent by the source satellite can be expressed as:

[0126]

[0127] Target satellite S m The amount of data sent is:

[0128]

[0129] Among them, t ho Indicates the duration of this phase.

[0130] The total amount of data received by the user can be expressed as:

[0131]

[0132] The ratio of duplicate data packets can be obtained by using the above formula for the amount of data received by the target satellite:

[0133]

[0134] From this, we can calculate u k The effective data volume is expressed as:

[0135]

[0136] Then, the downlink rate of the user in the handover execution phase can be expressed as:

[0137]

[0138] Although the dual active protocol stack (DAPS) strategy can eliminate the interruption time during the handover process, it may introduce additional delay T because the user needs to reorder the received data packets at the PDCP layer. DAPS .

[0139] Due to the complexity and variability of the network conditions between the satellite and the user, during the DAPS switching execution phase, the data packets of the two downlinks cannot be guaranteed to arrive at the user in sequence. DAPS There is an upper bound, which is defined as the source satellite S n and the target satellite S m The maximum difference between nodes' expected downstream delays is expressed as:

[0140] T DAPS ≤|E[T S-Sat ]-E[T T-Sat ]|

[0141] in, Unlike ground networks, the Xn interface between satellites does not rely on stable fiber connections, but uses unstable intersatellite links. Therefore, the target satellite downlink delay in this paper needs to take into account the intersatellite link delay T Xn , the downlink delay of the target satellite can be expressed as:

[0142]

[0143] Among them, E[T S-Sat ] represents the source satellite S n The expected downlink delay is Represents user u k With satellite S n Downlink outage probability, Represents user u k With satellite S n Downlink transmission delay, Represents user u k With satellite S n The downlink transmission delay of the target satellite takes into account the inter-satellite link delay T Xn , the expected downlink delay of the target satellite E[T T-Sat ] is expressed as:

[0144]

[0145] Represents user u k With satellite S m Downlink outage probability, Represents user u k With satellite S m Downlink transmission delay, Represents user u k With satellite S m Downlink transmission delay for retransmission via the HARQ entity;

[0146] Connection interruption probability P out It is defined as the signal-to-noise ratio (SNR) of the user equipment in the satellite-user transmission is lower than the predetermined threshold γ th This indicator reflects the reliability of service quality in communication, and its expression is:

[0147]

[0148] To simplify the representation, define a new variable:

[0149]

[0150] Therefore, X~Exp(Y k),in The connection interruption probability can be further expressed as:

[0151]

[0152] This outage probability depends only on the channel conditions and does not take into account distance or other time-varying factors. Due to the high altitude of the satellite, the propagation delay between the user and the satellite is much greater than the transmission delay. Therefore, the downlink delay T 1 It is mainly determined by the propagation delay. Under the hybrid automatic repeat request (HARQ) mechanism, if a data packet is retransmitted once, the downlink delay T 2 It can be expressed as Where c represents the speed of light.

[0153] In order to ensure that the downlink delay of DAPS switching is lower than the downlink delay of the traditional switching strategy, the following inequality needs to be satisfied:

[0154] maxT DAPS ≤T HIT

[0155] Specifically:

[0156]

[0157] In combination with the above analysis, the present invention constructs an optimization problem, whose objective function is to maximize the average downlink rate of all users:

[0158]

[0159] Among them, C1.1 indicates the user of the integrated dual-activation protocol stack The switching strategy for the dual-active switching strategy is used, while the remaining users use the traditional switching strategy. C1.2 stipulates that the bandwidth allocation for the service users must meet the minimum guarantee requirements. C1.3 and C1.4 specify that each user can only switch to one target satellite at the same time, and the source satellite and the target satellite must be different. In addition, constraint C1.5 ensures that the total bandwidth allocated to each satellite does not exceed its available bandwidth limit. C1.6 and C1.7 define the conditions for the use of the dual-active switching strategy, where C1.6 ensures that the target satellite can handle data loads exceeding a predetermined threshold, while C1.7 sets an upper limit on the packet reordering delay at the PDCP layer.

[0160] S2. Design a multi-stage handover mechanism for low-orbit satellite networks, including: state acquisition phase, satellites measure signal strength and exchange information; target satellite selection phase, select the best handover target satellite based on local state information to ensure seamless connection; handover execution phase, users maintain downlink connections with the service satellite and target satellite to minimize handover interruption; data transmission phase, satellites continue to transmit data to users;

[0161] Since the dynamics of the network affect the design of the model, it is difficult to solve it directly. Therefore, the present invention proposes a design method based on time frames. It is assumed that the satellite topology remains stable within a single time frame, and the length of each time frame is fixed to Δt.

[0162] The time frame is divided into the following four phases:

[0163] 1. Status acquisition phase: In this phase, each satellite measures the signal strength of its service users and exchanges relevant signal information with neighboring satellites to obtain the global network status.

[0164] 2. Target satellite selection phase: Each satellite independently determines the next-hop switching satellite based on local state information and completes the execution of the switching decision at the end of the phase.

[0165] 3. Handover execution phase: Based on the handover decision, the user equipment (UE) establishes a downlink connection with the target satellite. The duration of this phase is t ho , used to complete the switching execution and the exchange of related protocols.

[0166] 4. Data transmission phase: During this phase, each LEO satellite continuously transmits data to its service users. To ensure uninterrupted service, this phase will last until the next status acquisition phase begins.

[0167] If within a time frame, satellite S n According to the measurement results of the target satellite selection phase, the user u k If no handover is required, the handover execution phase will not be initiated and the user's downlink data transmission will continue to be provided by the satellite.

[0168] S3, based on the multi-stage switching mechanism, decompose the original optimization problem constructed in S1 into a bandwidth allocation sub-problem and a switching strategy sub-problem;

[0169] The model mentioned in S1 of the present invention is a mixed integer nonlinear programming (MINLP) problem. In order to reduce the computational complexity, the present invention simplifies it in the following way: First, Relaxation is a continuous variable with a range of [-1,1]; secondly, a new variable is introduced and represents the positive and negative parts of the slack variable; finally, the optimization problem is restructured and decomposed into two sub-problems: bandwidth allocation problem and switching strategy problem.

[0170] The slack variable can be understood as the time required for the user to connect to the target satellite after executing the switching decision. Therefore, the optimization problem in S1 can be rewritten as:

[0171]

[0172] The core of bandwidth allocation is to reasonably allocate available communication resources among users based on factors such as the satellite's bandwidth capacity and user needs. The focus of the switching strategy is to ensure the continuity of communication by selecting the best satellite for each user. Bandwidth allocation mainly solves the problem of resource sharing and optimization under fixed network topology, while the switching strategy dynamically adjusts the connection relationship between users and satellites based on mobility and signal condition changes. Although the two complement each other, they are independent processes, each facing different challenges, which need to be solved by different algorithms and optimization techniques.

[0173] Therefore, one method to simplify the problem is to optimize the optimal solution of the two groups of variables in sequence. The present invention decomposes the original problem into two independent sub-problems for solution by fixing the switching strategy variable and the bandwidth allocation variable respectively.

[0174] The original optimization problem can be simplified as:

[0175]

[0176] stC2.3,C2.6,C2.7

[0177] When the given switching variable ξ is not feasible, there may not be any b that can simultaneously satisfy the constraints C2.3, C2.6 and C3.7. In this case, the present invention sets the objective function value J * (ξ) is defined as -∞. Since only b is a free variable in the simplified optimization problem, this problem is called the Bandwidth Allocation (BA) problem.

[0178] Then, based on the solution of the bandwidth allocation sub-problem, the switching strategy (DAPS switching, DH) sub-problem is further obtained:

[0179]

[0180] stC2.1,C2.2,C2.4~C2.8

[0181] S4. For the bandwidth allocation sub-problem, the alternating direction method of multipliers (ADMM) is used to solve it. This distributed optimization algorithm decomposes the global optimization problem into multiple sub-problems and allows each sub-problem to be solved independently. Each satellite independently calculates the optimal bandwidth allocation solution based on its own bandwidth resources, user needs and network status;

[0182] In the bandwidth allocation (BA) problem proposed by the present invention, it can be proved that the bandwidth allocation sub-problem is a convex optimization problem through analysis of the problem. When fixed, the optimization variable only includes bandwidth allocation First, consider the objective function, which is an affine function of the bandwidth allocation variables and is therefore convex. For constraints C2.3, C2.6, and C2.7, they are linear functions of b and are therefore convex. Since the objective function and all constraints are convex, we can conclude that the bandwidth allocation subproblem is The fixed case is a convex optimization problem.

[0183] The distributed algorithm based on the alternating direction method of multipliers (ADMM) proposed in the present invention decomposes the problem into multiple sub-problems, each sub-problem involves only one satellite, and solves the global optimization problem through the coordination of local variables.

[0184] S5: For the switching strategy optimization sub-problem, the simulated annealing algorithm is used to solve it. By iteratively adjusting the switching strategy and accepting a worse solution with a certain probability, it avoids falling into the local optimal solution and finally finds the global optimal solution;

[0185] In each iteration, the simulated annealing algorithm randomly selects a neighborhood solution of the current strategy and calculates the objective function value corresponding to the solution. If the objective function value of the neighborhood solution is better than the current solution, the solution is directly accepted; otherwise, the worse solution is accepted based on the control probability of the current temperature. As the algorithm iterates, the temperature gradually decreases, reducing the probability of accepting a worse solution, thereby exploring the optimal switching strategy from a global perspective and avoiding the algorithm from falling into a local optimal solution.

[0186] The advantage of this method is that it can handle complex nonlinear and non-convex optimization problems, and is particularly suitable for handling the optimization problem of switching strategies in low-orbit satellite networks. Through the iterative search of the simulated annealing algorithm, the network performance can be effectively improved, ensuring that the user equipment has the least interruption time during the switching process and maintaining high-speed services.

[0187] S6. By solving the bandwidth allocation and switching strategy optimization sub-problems separately, the final optimization solution can be obtained, so as to maximize the average rate of the UE and minimize the switching interruption time, thereby improving the performance and user experience of the low-orbit satellite network;

[0188] Through the design of time frames in S2, each satellite in the network will independently optimize bandwidth allocation and switching strategies according to the current network status and user needs. In each time frame, the system solves the two sub-problems of bandwidth allocation and switching strategy optimization respectively. The solution of each sub-problem is carried out independently, but through precise coordination and feedback mechanisms, it is ensured that the solutions of the two sub-problems can cooperate with each other to achieve the overall optimal solution. Specifically, bandwidth allocation optimization dynamically adjusts resource allocation by considering the bandwidth resources and user needs of each satellite, while switching strategy optimization adjusts switching decisions to minimize interruption time according to the current network status and user location.

[0189] In the present invention, a greedy reduction method is used to reduce the slack variable ξ based on the solution results of the bandwidth allocation and switching strategy optimization problem. Specifically, the size of ξ is first determined. When the value of ξ is not equal to 0, if it is greater than 0, it is taken as 1; if it is less than 0, it is taken as -1. Next, the reduced ξ value is brought back to the constraint conditions for verification. If the constraint conditions are met, the reduction process is completed. Otherwise, the above operation is continued until a switching strategy ξ that meets the constraint requirements is finally obtained.

[0190] In the above process, the system will dynamically adjust the solution strategy based on real-time feedback information to adapt to changes in network status and user needs. In this way, the low-orbit satellite network can maintain optimal performance in a dynamically changing environment, thereby ensuring efficient use of network resources and continuous optimization of user experience.

[0191] Finally, by combining the results of bandwidth allocation and switching strategy optimization, the overall performance of the low-orbit satellite network can be significantly improved. By maximizing the average rate of user equipment and minimizing the switching interruption time, the system can not only ensure the downlink rate of users, but also improve the efficiency of network resource utilization.

[0192] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solution of the present invention can be modified or replaced by equivalents without departing from the purpose and scope of the technical solution, which should be included in the scope of the claims of the present invention.

Claims

1. A low-orbit satellite switching method based on a dual-activation protocol stack, characterized in that: The method comprises the following steps: S1. Establish a non-terrestrial network in a low-orbit satellite network environment, design a switching architecture based on a dual-active protocol stack with the optimization objectives of maximizing the average rate of user equipment and minimizing the switching interruption delay, and establish the original optimization problem; S2. Establish a multi-stage handover mechanism for the low-orbit satellite network, which at least includes a state acquisition stage, a target satellite selection stage, a handover execution stage, and a data transmission stage; S3, based on the established multi-stage switching mechanism, the original optimization problem is decomposed into a bandwidth allocation sub-problem and a switching strategy sub-problem; S4, using the alternating direction multiplier method to solve the bandwidth allocation subproblem; S5. Using simulated degradation algorithm to solve the switching strategy sub-problem; S6. Combine the solution results of the bandwidth allocation subproblem and the switching strategy subproblem to obtain the final optimal solution.

2. The low-orbit satellite switching method based on a dual-activation protocol stack according to claim 1, characterized in that: In step S1, the established non-terrestrial network includes N satellites and K users, and a time frame structure is designed, where the length of each frame is Δt, and the switching interruption delay is t ho ; Adopt a collection Represents the N satellites in the satellite constellation, the set represents the set of all users, and the users are randomly distributed within the coverage of N satellites. The user set is divided into users supporting the switching strategy based on the dual-activation protocol stack and users using the traditional switching strategy. The user set supporting the dual-activation protocol stack is Design correlation index xk,n t Describe user u k With satellite S n During the switching process, the connection status When the satellite S n Is user u k The service satellite of the target satellite S m set up To capture the associated transfer status after the switch is completed; use Represents the switching strategy, and its value is [-1,0,1], where Represents user u k Use the dual-activation switching strategy to switch to the target satellite S n ; Indicates that the user maintains the current connection status and does not switch; Represents user u k Use the traditional switching strategy to switch to the target satellite S n , interruption delay is allowed; Assume that at time t, satellite S n For user u k The allocated bandwidth is It satisfies the following bandwidth allocation constraints: In the formula, B n is the maximum bandwidth of each satellite; A channel model between the satellite and the user is established, which includes path loss and Rayleigh fading. The path loss is calculated as: Where c is the speed of light, is the distance between UE and satellite, f is the carrier frequency; Channel Vector represents the channel response from the satellite to the UE, which follows Rayleigh fading and is a circularly symmetric complex Gaussian random variable with zero mean and unit variance. Under Rayleigh fading conditions, the signal-to-noise ratio (SNR) and the channel gain Related, the calculation formula of SNR is: Where P A represents the satellite's transmission power, and N0 is the noise power; Then we have: In the formula, For user u k At time t from satellite S n Received downlink rate.

3. The low-orbit satellite switching method based on a dual-activation protocol stack according to claim 2, characterized in that: In the established handover architecture based on the dual-activation protocol stack, the handover strategy based on the dual-activation protocol stack allows the user equipment UE to maintain downlink connections with two satellites at the same time during the handover execution phase. In this phase, the source satellite continues to allocate downlink packet data convergence protocol layer sequence numbers SN until the allocation task is officially handed over to the target satellite. The target satellite receives and retransmits all downlink data forwarded by the source satellite through the Xn interface, prioritizes all downlink data, and then forwards the downlink PDCP SDU that does not contain the sequence number SN; In the handover execution phase, the downlink data received by the user includes the superimposed data of the source and target satellites, as well as the protocol processing data; Among them, the amount of data received by the target satellite is expressed as: Where α is the implementation loss factor, which is used to adjust the difference between the theoretical maximum data rate and the actual implementation rate; Indicates satellite S m Load; represents the number of users switched to the target satellite; t interval is the data request interval, t off The data request lead time offset is used to request data in advance; Assume that the amount of data sent by the source satellite is expressed as: Target satellite S m The amount of data sent is: In the formula, t ho Indicates the duration of the phase; Then, the total amount of data received by the user is expressed as: Calculate the ratio of packets: Calculate u k The effective amount of data: The downlink rate of the user during the handover execution phase is expressed as: Introducing an additional delay T DAPS Reorder the received data packets with a reordering delay T DAPS There is an upper bound, which is defined as the source satellite S n and the target satellite S m The maximum difference between nodes’ expected downstream delays is expressed as: T DAPS ≤|E[T S-Sat ]-E[T T-Sat ]| Among them, E[T S-Sat ] represents the source satellite S n The expected downlink delay is Represents user u k With satellite S n Downlink outage probability, Represents user u k With satellite S n Downlink transmission delay, Represents user u k With satellite S n The downlink transmission delay of the target satellite takes into account the inter-satellite link delay T Xn , the expected downlink delay of the target satellite E[T T-Sat ] is expressed as: Represents user u k With satellite S m Downlink outage probability, Represents user u k With satellite S m Downlink transmission delay, Represents user u k With satellite S m Downlink transmission delay for retransmission via the HARQ entity; Connection interruption probability P out It is defined as the signal-to-noise ratio of the user equipment in the satellite-user transmission is lower than the predetermined threshold γ th The probability of is expressed as: Define a new variable: Then X~Exp(Y k ),in The connection interruption probability is further expressed as: Downlink delay T 1 Mainly determined by the propagation delay, under the hybrid automatic repeat request mechanism, if a data packet is retransmitted once, the downlink delay T 2 Expressed as Where c represents the speed of light; The downlink delay of DAPS switching is lower than that of the traditional switching strategy, satisfying the following inequality: maxT DAPS ≤T HIT Right now: Among them, T HIT is the downlink delay of the traditional switching strategy.

4. The low-orbit satellite switching method based on a dual-activation protocol stack according to claim 3, characterized in that: According to the established switching architecture based on the dual-active protocol stack, the original optimization problem P1 established with the optimization objectives of maximizing the average rate of the user equipment and minimizing the switching interruption delay is expressed as: Among them, C1.1 indicates the user of the integrated dual-activation protocol stack switching strategy, while the rest of the users use the traditional switching strategy; C1.2 stipulates that the bandwidth allocation of the service users meets the minimum guarantee requirements; C1.3 and C1.4 specify that each user can only switch to one target satellite at the same time, and the source satellite and the target satellite are different; C1.5 ensures that the total bandwidth allocated to each satellite does not exceed its available bandwidth limit; C1.6 and C1.7 define the conditions for the use of the dual-activation switching strategy, among which C1.6 ensures that the target satellite can handle data loads exceeding a predetermined threshold, and C1.7 sets an upper limit for the packet reordering delay at the PDCP layer.

5. The low-orbit satellite switching method based on a dual-activation protocol stack according to claim 4, characterized in that: In step S2, in the established multi-stage switching mechanism of the low-orbit satellite network, the satellite topology remains stable within a single time frame, the length of each time frame is fixed to Δt, and each time frame is divided into the following four stages: Status acquisition phase: Each satellite measures the signal strength of its service users and exchanges relevant signal information with neighboring satellites to obtain the global network status; Target satellite selection phase: Each satellite independently determines the best target satellite for the next hop handover based on local status information; Handover execution phase: According to the handover decision, the user equipment UE establishes a downlink connection with the target satellite. The duration of this phase is t ho , used to complete the switching execution and the exchange of related protocols; Data transmission phase: During this phase, each source satellite continuously transmits data to its service users. This phase will last until the next status acquisition phase begins; If within a time frame, satellite S n According to the measurement results of the target satellite selection phase, the user u k If no handover is required, the handover execution phase will not be initiated and the user's downlink data transmission will continue to be provided by the satellite.

6. A low-orbit satellite switching method based on a dual-activation protocol stack according to claim 5, characterized in that: In step S3, first Relaxation is a continuous variable with a range of [-1,1]; secondly, a new variable is introduced and represents the positive and negative parts of the slack variable; finally, the optimization problem is restructured and decomposed into the bandwidth allocation problem and the switching strategy problem; among them, The slack variable is the time required for the user to connect to the target satellite after executing the switching decision. The original optimization problem P1 is optimized to P2: By fixing the switching strategy variables and bandwidth allocation variables respectively, the original problem is decomposed into two independent sub-problems for solution, where the objective function value J * (ξ) is defined as -∞, and only b is taken as a free variable, and the bandwidth allocation subproblem is obtained: stC2.3,C2.6,C2.7 Then, based on the solution of the bandwidth allocation subproblem, the switching strategy subproblem is further obtained: stC2.1,C2.2,C2.4~C2.8 Where ξ is the independent variable of the switching strategy subproblem.

7. The low-orbit satellite switching method based on a dual-activation protocol stack according to claim 6, characterized in that: In step S4, the bandwidth allocation subproblem is solved in the switching strategy In the fixed case, it is a convex optimization problem. A distributed algorithm based on the alternating direction multiplier method is used to decompose the problem into multiple subproblems, each of which involves only one satellite, and the global optimization problem is solved by coordinating local variables.

8. The low-orbit satellite switching method based on a dual-activation protocol stack according to claim 7, characterized in that: In step S5, the simulated annealing algorithm is used to solve the switching strategy optimization sub-problem, by iteratively adjusting the switching strategy and accepting non-optimal solutions according to a preset probability to avoid falling into the local optimum, and finally finding the global optimal solution; In each iteration, the simulated annealing algorithm randomly selects a neighborhood solution of the current strategy and calculates the objective function value corresponding to the solution. If the objective function value of the neighborhood solution is better than the current solution, the solution is directly accepted; otherwise, the non-optimal solution is accepted based on the control probability of the current temperature. As the algorithm iterates, the temperature gradually decreases, reducing the probability of accepting non-optimal solutions, thereby exploring the optimal switching strategy from a global perspective.

9. The low-orbit satellite switching method based on a dual-activation protocol stack according to claim 8, characterized in that: In step S6, the bandwidth allocation and handover strategy optimization sub-problems are solved separately to obtain a final optimization solution, so as to maximize the average rate of the UE and minimize the handover interruption time; In each time frame, the system solves the bandwidth allocation and switching strategy optimization sub-problems respectively. The solution of each sub-problem is carried out independently, and a coordination and feedback mechanism is established between the two. The bandwidth allocation optimization dynamically adjusts the resource allocation by considering the bandwidth resources and user needs of each satellite, while the switching strategy optimization adjusts the switching decision to minimize the interruption time according to the current network status and user location.

10. A low-orbit satellite switching method based on a dual-activation protocol stack according to claim 9, characterized in that: In step S6, a greedy reduction method is used to reduce the slack variable ξ according to the solution of the bandwidth allocation and switching strategy optimization problem. The process is as follows: First, determine the size of ξ. When the value of ξ is not equal to 0, if it is greater than 0, it is set to 1. If it is less than 0, it is taken as -1; Then bring the restored ξ value back to the constraint conditions for verification. If the constraint conditions are met, the restoration process is completed. Otherwise, continue the above operation until a switching strategy ξ that meets the constraint requirements is finally obtained.

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