Low earth orbit satellite handover method based on dual active protocol stack

Abstract

The present application relates to a kind of low-orbit satellite switching methods based on double activation protocol stack, belong to satellite mobile communication technical field.The method includes: in low-orbit satellite network environment, design with the average rate of user equipment maximization and the switching interruption delay minimization as optimization target's switching architecture based on double activation protocol stack, and establish original optimization problem;Establish low-orbit satellite network multi-stage switching mechanism;Based on the multi-stage switching mechanism established, original optimization problem is decomposed into bandwidth allocation sub-problem and switching strategy sub-problem;Bandwidth allocation sub-problem is solved using alternate direction multiplier method;Switching strategy sub-problem is solved using simulated annealing algorithm;The final optimal solution is obtained by combining the solving results of bandwidth allocation sub-problem and switching strategy sub-problem.The present application can effectively deal with the challenge of frequent satellite switching and limited satellite resources in satellite network, while realizing high-speed, seamless connection, and improving user experience.

Description

Technical Field

[0001] This invention belongs to the field of satellite mobile communication technology and relates to a low-orbit satellite handover method based on a dual-activation protocol stack. Background Technology

[0002] Non-terrestrial networks (NTNs), as a powerful complement to wireless and fixed terrestrial communications, have become an important component of the 5G era and the upcoming 6G era, providing ubiquitous connectivity for a wide range of devices and applications. Compared to traditional high-Earth orbit and medium-Earth orbit satellite constellations, emerging satellite networks are primarily composed of low Earth orbit (LEO) satellites. LEO satellite constellations offer significant advantages, including seamless service coverage and significantly reduced latency. 3GPP began exploring the possibility of providing network connectivity for user equipment (UEs) using satellites and airborne platforms in Release 15 and further advanced this work in Release 16, particularly by investigating how to adapt 5G New Radio (NR) to support non-terrestrial networks (NTNs).

[0003] Unlike fixed base stations in terrestrial networks, LEO satellites, operating at low Earth orbit (typically between 500 and 1200 kilometers), offer lower transmission latency and enhanced radio link budgets. However, these advantages also present challenges, particularly the highly dynamic nature of the connection between satellites and users, leading to frequent handovers during user service. Mobility management, especially handover management, is crucial to ensuring network connectivity and service continuity. Enhanced mobility support is a significant challenge in 5G mobile communication systems, with the ultimate goal of 5G networks achieving near-zero time-to-migration (MIT), the shortest possible time during handover when a user equipment (UE) cannot exchange user plane data packets with any base station (BS). MIT is defined as the sum of the recovery time in a handover failure (HOF) and the handover interruption time (HIT) in a successful handover (HO).

[0004] In recent years, 3GPP has proposed various 5G network mobility enhancement technologies aimed at minimizing the time-to-market (MIT) and improving handover efficiency. During handover (HO) based on the Dual Activation Protocol Stack (DAPS), the User Equipment (UE) maintains connections with both the source and target base stations simultaneously. To support this handover, the UE must activate two protocol stacks: one for the target cell (including the Physical Layer (PHY), Media Access Control (MAC), and Radio Link Control (RLC); and another for transmitting and receiving user data in the source cell.

[0005] However, existing mobility enhancement technologies based on terrestrial networks are not suitable for LEO satellite networks due to limited satellite resources and highly dynamic network topology. This further exacerbates the already limited service quality of satellite networks. Therefore, these research methods are difficult to effectively adapt to the LEO satellite communication scenario, and research on handover methods in satellite networks urgently needs to consider network dynamics while ensuring service quality. Summary of the Invention

[0006] In view of this, the purpose of this invention is to provide a low-Earth orbit satellite handover method based on a dual-activation protocol stack.

[0007] To achieve the above objectives, the present invention provides the following technical solution:

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

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

[0010] S2. Establish a multi-stage handover mechanism for low-Earth orbit satellite networks, including at least the status acquisition stage, target satellite selection stage, handover execution stage, and 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. The bandwidth allocation subproblem is solved using the alternating direction multiplier method.

[0013] S5. The switching strategy subproblem is solved using a simulated degradation algorithm.

[0014] S6. The final optimal solution is obtained by combining the solution results of the bandwidth allocation subproblem and the switching strategy subproblem.

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

[0016] Using sets This represents the N satellites in a satellite constellation, a set. Let N represent the set of all users, randomly distributed within the coverage area of ​​N satellites. The user set is divided into those supporting a handover strategy based on the dual-activation protocol stack and those using a traditional handover strategy. The set of users supporting the dual-activation protocol stack is...

[0017] Design correlation indicators xk,n t Describe user u k With satellite S n During the handover process, the connection status when At that time, it indicates that satellite S n User u k The service satellites, with a downlink between them; the target satellite S m set up To capture the associated transfer status after the switch is completed;

[0018] use This represents the switching strategy, with values ​​ranging from [-1, 0, 1]. Indicates user u k A dual-activation handover strategy is adopted to switch to the target satellite S. n ; This indicates that the user should maintain the current connection state and not perform a switch. Indicates user u k Switching to target satellite S using traditional handover strategies n Interruption delays are allowed;

[0019] Let satellite S be at time t. n For user u k The allocated bandwidth is It meets the following bandwidth allocation constraints:

[0020]

[0021] In the formula, B n The maximum bandwidth for 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 follows:

[0023]

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

[0025] Channel vector The channel response from the satellite to the UE, following Rayleigh fading, is a circular 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 Related, the formula for calculating SNR:

[0027]

[0028] Where P A This represents the satellite's transmission power, with N0 being the noise power.

[0029] Then we have:

[0030]

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

[0032] Furthermore, 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 connection with both satellites simultaneously during the handover execution phase. During this phase, the source satellite continues to allocate downlink packet data aggregation protocol layer sequence number (SN) until the allocation task is officially 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 downlink PDCPSDUs that do not contain the sequence number SN.

[0034] During the handover execution phase, the downlink data received by the user includes superimposed data from the source satellite and the target satellite, as well as protocol processing data;

[0035] The amount of data received by the target satellite is represented as follows:

[0036]

[0037] In the formula, α represents the realization loss factor, which is used to adjust the difference between the theoretical maximum data rate and the actual realized rate; Indicates satellite S m The load; Indicates the number of users switching to the target satellite; t interval t is the data request interval. off This is the data request lead time offset, used to request data in advance;

[0038] Let the amount of data transmitted by the source satellite be expressed as:

[0039]

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

[0041]

[0042] In the formula, t hoIndicates the duration of this phase;

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

[0044]

[0045] Calculate the proportion of data packets:

[0046]

[0047] Calculate u k Effective data volume:

[0048]

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

[0050]

[0051] Introducing an additional delay T DAPS The received data packets are reordered, with a reordering delay T. DAPS There exists an upper bound, defined as source satellite S n and target satellite S m The maximum difference between the expected downlink latency of nodes is expressed as:

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

[0053] Among them, E[T S-Sat ] indicates source satellite S n The expected downlink delay Indicates user u k With satellite S n Downlink interruption probability, Indicates user u k With satellite S n Downlink transmission delay Indicates user u k With satellite S n Downlink transmission delay via HARQ entity for retransmission; target satellite downlink delay considering inter-satellite link delay T. Xn The expected downlink delay E[T] of the target satellite T-Sat ] is represented as:

[0054]

[0055] Indicates user u k With satellite Sm Downlink interruption probability, Indicates user u k With satellite S m Downlink transmission delay Indicates user u k With satellite S m Downlink transmission delay when retransmitted via HARQ entity;

[0056] Connection interruption probability P out Defined as when the signal-to-noise ratio of user equipment in satellite-to-user transmission is lower than a 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 probability of connection interruption can be further expressed as:

[0061]

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

[0063] The downlink latency of DAPS handover is lower than that of traditional handover strategies, satisfying the following inequality:

[0064] maxT DAPS ≤T HIT

[0065] Right now:

[0066]

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

[0068] Furthermore, based on the established handover architecture using a dual-activation protocol stack, the original optimization problem P1, with the optimization objectives of maximizing the average rate of user equipment and minimizing handover interruption latency, is expressed as:

[0069]

[0070] C1.1 represents the user integrating the dual-activation protocol stack. The switching strategy for the first user is as follows: C1.2 specifies that the bandwidth allocation for the service user meets the minimum guarantee requirements; C1.3 and C1.4 specify that each user can only switch to one target satellite at a time, and require that 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 limit the conditions for using the dual-active switching strategy, where 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 of the PDCP layer.

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

[0072] Status acquisition phase: Each satellite measures the signal strength of the users it serves 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 its local status information;

[0074] Handover Execution Phase: Based on the handover decision, the User Equipment (UE) establishes a downlink connection with the target satellite. This phase lasts for t seconds. ho It is 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 continue until the start of the next status acquisition phase.

[0076] If within a time frame, satellite S n The decision regarding user u is based on the measurement results during the target satellite selection phase. 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 this satellite.

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

[0078] The slack variable is the time required for the user to connect to the target satellite after making a handover decision. Therefore, the original optimization problem P1 is optimized to P2:

[0079]

[0080] By fixing the switching strategy variable and the bandwidth allocation variable respectively, the original problem is decomposed into two independent subproblems for solution. The objective function value J is... * Define (ξ) as -∞, and with only b as a free variable, we obtain the bandwidth allocation subproblem:

[0081]

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

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

[0084]

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

[0086] In the formula, ξ is the independent variable of the switching strategy subproblem.

[0087] Furthermore, in step S4, the bandwidth allocation sub-problem is addressed in the switching strategy. Under fixed conditions, 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 subproblem involves only one satellite, and the global optimization problem is solved by coordinating local variables.

[0088] Furthermore, in step S5, the simulated annealing algorithm is used to solve the switching strategy optimization subproblem. By iteratively adjusting the switching strategy and accepting non-optimal solutions according to a preset probability, the solution is avoided from getting trapped in local optima and finally the global optimal solution is found.

[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 that of the current solution, the solution is accepted directly; otherwise, a non-optimal solution is accepted based on the control probability of the current temperature. As the algorithm iterates, the temperature gradually decreases, which reduces the probability of accepting a non-optimal solution, thus realizing the exploration of the optimal switching strategy from a global perspective.

[0090] Furthermore, in step S6, the final optimized solution is obtained by solving the bandwidth allocation and handover strategy optimization sub-problems respectively, thereby maximizing the average rate of the UE and minimizing the handover interruption time.

[0091] Within each time frame, the system solves the bandwidth allocation and handover strategy optimization sub-problems independently, and establishes a coordination and feedback mechanism between the two. The bandwidth allocation optimization dynamically adjusts resource allocation by considering the bandwidth resources of each satellite and user needs, while the handover strategy optimization adjusts handover decisions based on the current network status and user location to minimize downtime.

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

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

[0094] The restored ξ value is then brought back to the constraints for verification. If the constraints are satisfied, the restoration process is complete; otherwise, the above operation continues until a switching strategy ξ that meets the constraints is finally obtained.

[0095] The beneficial effects of this invention are as follows:

[0096] This invention fully considers the high dynamism and resource allocation issues in low Earth orbit (LEO) satellite networks and proposes a handover method based on a dual-activation protocol stack (DAPS). This method maintains the connection between the user equipment (UE) and both the source and target base stations during the handover process and employs a distributed optimization strategy, effectively ensuring high downlink rates for users while maintaining low handover interruption latency.

[0097] Other advantages, objectives, and features of the invention will be set forth in part in the description which follows, and in part will be apparent to those skilled in the art from the following examination, or may be learned from practice of the invention. The objectives and other advantages of the invention can be realized and obtained through the following description. Attached Figure Description

[0098] To make the objectives, technical solutions, and advantages of the present invention clearer, the preferred embodiments of the present invention will be described in detail below with reference to the accompanying drawings, wherein:

[0099] Figure 1 This is an overall flowchart of the low-Earth orbit satellite handover method based on a dual-activation protocol stack according to the present invention;

[0100] Figure 2 This is a schematic diagram illustrating the dual-activation stack switching process in the satellite network according to the present invention. Detailed Implementation

[0101] The following specific examples illustrate the implementation of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and various details in this specification can be modified or changed 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 are only schematic representations of the basic concept of the present invention. Unless otherwise specified, the following embodiments and features can be combined with each other.

[0102] The accompanying drawings are for illustrative purposes only and are schematic diagrams, not actual pictures. They should not be construed as limiting the invention. To better illustrate the embodiments of the invention, some parts in the drawings may be omitted, enlarged, or reduced, and do not represent the actual product dimensions. It is understandable to those skilled in the art that some well-known structures and their descriptions may be omitted in the drawings.

[0103] In the accompanying drawings of the embodiments of the present invention, the same or similar reference numerals correspond to the same or similar components. In the description of the present invention, it should be understood that if terms such as "upper," "lower," "left," "right," "front," and "rear" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings, they are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, the terms used to describe positional relationships in the drawings are only for illustrative purposes and should not be construed as limiting the present invention. For those skilled in the art, the specific meaning of the above terms can be understood according to the specific circumstances.

[0104] Please see Figures 1-2 This is a low-Earth orbit satellite handover method based on a dual-activation protocol stack.

[0105] Example

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

[0107] S1. In a low-Earth orbit satellite network environment, this study aims to construct a handover architecture based on a dual-active protocol stack (DAPS) by optimizing network throughput and minimizing handover interruption latency. This architecture comprehensively considers key factors such as handover interruption time and user rate, and constructs a primitive 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 each frame has a length of Δt, and the handover interruption delay is t.ho .gather This represents the N satellites in a satellite constellation, a set. This represents the set of all users, randomly distributed across the coverage area of ​​N satellites. The set of users supporting Dual Activation Protocol Stack (DAPS) is... The remaining users adopt the traditional handover strategy, which allows for a certain handover interruption delay.

[0109] Within each coverage area, since each user may be covered by multiple satellites, the correlation metric xk,n during Dual Activation Protocol Stack (DAPS) handover... t Used to describe user u k With satellite S n Connection status during the handover process. When At that time, it indicates that satellite S n User u k The service satellites of the target satellite S have a downlink between them. m set up It can accurately capture the associated transfer status after the switch is completed.

[0110] make This represents the switching strategy, and its value range is [-1, 0, 1]. Indicates user u k A dual-activation handover strategy is adopted to switch to the target satellite S. n , This indicates that the user should maintain the current connection state and not perform a switch. Indicates user u k Use traditional handover strategies to switch to target satellite S n A certain interruption delay is allowed.

[0111] use Indicates that at time t, satellite S n For user u k The allocated bandwidth. Since the bandwidth of each satellite is limited, its maximum bandwidth is denoted as B. n Therefore, the following bandwidth allocation constraints can be obtained:

[0112]

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

[0114]

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

[0116] Channel vector The channel response from the satellite to the UE, following Rayleigh fading, is a circular 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 Relatedly, the formula for calculating SNR is:

[0118]

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

[0120]

[0121] Unlike traditional handover strategies in wireless networks, the handover strategy based on a dual-activation protocol stack allows the User Equipment (UE) to maintain downlink connections with both satellites simultaneously during the handover execution phase. During this phase, the source satellite continues to assign downlink Packet Data Convergence Protocol (PDCP) layer sequence numbers (SNs) until the assignment task is formally handed over to the target satellite. Furthermore, the target satellite receives and retransmits all downlink data forwarded by the source satellite via the Xn interface, prioritizing this data before forwarding downlink PDCP SDUs that do not contain sequence numbers (SNs). During the handover execution phase, the downlink data received by the user not only simply overlays data from both satellites but also involves complex protocol processing.

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

[0123]

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

[0125] To study user u kUnder the dual-activation protocol stack switching strategy, there is a rate issue with two downlinks during the switching execution phase. First, assume that the amount of data transmitted 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 This indicates the duration of the phase.

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

[0131]

[0132] Using the formula for the amount of data received by the target satellite mentioned above, the proportion of duplicate data packets can be obtained:

[0133]

[0134] Therefore, u can be calculated. k The effective data volume is represented as:

[0135]

[0136] Next, the downlink rate during the user's switching execution phase can be expressed as:

[0137]

[0138] Although the Dual Activation Protocol Stack (DAPS) strategy can eliminate interruption time during handover, the need for users to reorder received packets at the PDCP layer may introduce additional latency T. DAPS .

[0139] Due to the complexity and variability of network conditions between the satellite and the user, during the DAPS handover execution phase, data packets from the two downlinks cannot be guaranteed to arrive at the user in the correct order. Reordering delay T DAPS There exists an upper bound, defined as source satellite S n and target satellite S m The maximum difference between the expected downlink latency of nodes is specifically expressed as:

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

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

[0142]

[0143] Among them, E[T S-Sat ] indicates source satellite S n The expected downlink delay Indicates user u k With satellite S n Downlink interruption probability, Indicates user u k With satellite S n Downlink transmission delay Indicates user u k With satellite S n Downlink transmission delay via HARQ entity for retransmission; target satellite downlink delay considering inter-satellite link delay T. Xn The expected downlink delay E[T] of the target satellite T-Sat ] is represented as:

[0144]

[0145] Indicates user u k With satellite S m Downlink interruption probability, Indicates user u k With satellite S m Downlink transmission delay Indicates user u k With satellite S m Downlink transmission delay when retransmitted via HARQ entity;

[0146] Connection interruption probability P out Defined as when the signal-to-noise ratio (SNR) of a user equipment in satellite-to-user transmission is lower than a predetermined threshold γ. th The probability of [something]. 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 probability of connection interruption can be further expressed as:

[0151]

[0152] This outage probability depends solely on channel conditions, without considering distance or other time-varying factors. Due to the satellite's high altitude, the propagation delay between the user and the satellite is much greater than the transmission delay; therefore, the downlink delay T in this study... 1 Primarily determined by 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 represented as Where c represents the speed of light.

[0153] To ensure that the downlink latency of DAPS handover is lower than that of traditional handover strategies, the following inequality must be satisfied:

[0154] maxT DAPS ≤T HIT

[0155] Specifically:

[0156]

[0157] Based on the above analysis, this invention constructs an optimization problem with the objective function of maximizing the average downlink rate for all users:

[0158]

[0159] C1.1 represents the user integrating the dual-activation protocol stack. The switching strategy for one user is as follows: The source satellite is used by one user, while the other users use the traditional switching strategy. C1.2 specifies that bandwidth allocation for serving users must meet minimum guarantee requirements. C1.3 and C1.4 specify that each user can only switch to one target satellite at a time, and require that the source satellite and target satellite be different. Furthermore, 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 using 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 packet reordering latency at the PDCP layer.

[0160] S2. Design a multi-stage handover mechanism for a low-Earth orbit satellite network, comprising: a status acquisition stage, in which the satellite measures signal strength and exchanges information; a target satellite selection stage, in which the best target satellite for handover is selected based on local status information to ensure seamless connection; a handover execution stage, in which the user maintains downlink connections with the serving satellite and the target satellite to minimize handover interruptions; and a data transmission stage, in which the satellite continuously transmits data to the user.

[0161] Due to the dynamic nature of the network, the design of the model is difficult, making direct solutions challenging. Therefore, this invention proposes a time-frame-based design method. It is assumed that the satellite topology remains stable within a single time frame, and the length of each time frame is fixed at Δt.

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

[0163] 1. Status Acquisition Phase: In this phase, each satellite measures the signal strength of its served 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 satellite based on its local status information and completes the execution of the handover 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 It is 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 continues until the start of the next status acquisition phase.

[0167] If within a time frame, satellite S n The decision regarding user u is based on the measurement results during the target satellite selection phase. 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 this satellite.

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

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

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

[0171]

[0172] The core of bandwidth allocation lies in rationally allocating available communication resources among users based on factors such as satellite bandwidth capacity and user demand. Handover strategy, on the other hand, focuses on ensuring communication continuity by selecting the optimal satellite for each user. Bandwidth allocation primarily addresses resource sharing and optimization issues in fixed network topologies, while handover strategy dynamically adjusts the connection between users and satellites to accommodate changes in mobility and signal conditions. Although complementary, they are independent processes, each facing different challenges and requiring different algorithms and optimization techniques to address.

[0173] Therefore, one way to simplify the problem is to sequentially optimize the optimal solutions for the two sets of variables. This invention decomposes the original problem into two independent subproblems by fixing the switching strategy variable and the bandwidth allocation variable respectively.

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

[0175]

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

[0177] When the given switching variable ξ is infeasible, there may not be any b that can simultaneously satisfy constraints C2.3, C2.6, and C3.7. In this case, the present invention will set 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 to the bandwidth allocation subproblem, the switching strategy (DAPS switching, DH) subproblem is further obtained:

[0179]

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

[0181] S4. For the bandwidth allocation subproblem, the Alternating Directional Multiplier Method (ADMM) is used for solution. This distributed optimization algorithm decomposes the global optimization problem into multiple subproblems and allows each subproblem to be solved independently. Each satellite independently calculates the optimal bandwidth allocation scheme based on its own bandwidth resources, user needs, and network status.

[0182] In the bandwidth allocation (BA) problem proposed in this invention, analysis of the problem shows that the bandwidth allocation sub-problem is a convex optimization problem. When switching strategies... When fixed, the optimization variables only include bandwidth allocation. First, consider the objective function, which is an affine function of the bandwidth allocation variable, and therefore convex. Constraints C2.3, C2.6, and C2.7 are linear functions of b, and therefore convex. Since the objective function and all constraints are convex, we can conclude that the bandwidth allocation subproblem lies in the strategy switching... Under fixed conditions, it is a convex optimization problem.

[0183] The distributed algorithm based on the Alternating Direction Multiplier Method (ADMM) proposed in this invention decomposes the problem into multiple subproblems, each involving only one satellite, and solves the global optimization problem by coordinating local variables.

[0184] S5: For the switching strategy optimization subproblem, the simulated annealing algorithm is used to solve it. By iteratively adjusting the switching strategy and accepting a poor solution with a certain probability, the algorithm avoids getting trapped in local optima and eventually finds the global optimum.

[0185] In each iteration, the simulated annealing algorithm randomly selects a neighborhood solution of the current strategy and calculates the corresponding objective function value. If the objective function value of the neighborhood solution is better than that of the current solution, the solution is accepted directly; otherwise, a 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. This allows the algorithm to explore the optimal switching strategy from a global perspective and avoid getting trapped in local optima.

[0186] The advantage of this method lies in its ability to handle complex nonlinear and nonconvex optimization problems, making it particularly suitable for optimizing handover strategies in low-Earth orbit satellite networks. Through iterative search using the simulated annealing algorithm, network performance can be effectively improved, ensuring that user equipment experiences minimal downtime during handover and maintains high-speed service.

[0187] S6. By solving the bandwidth allocation and handover strategy optimization sub-problems separately, the final optimized solution can be obtained, which maximizes the average rate of the UE and minimizes the handover interruption time, thereby improving the performance and user experience of the low-Earth orbit satellite network.

[0188] Through the time frame design in S2, each satellite in the network independently optimizes bandwidth allocation and handover strategies based on the current network status and user needs. Within each time frame, the system solves two sub-problems: bandwidth allocation and handover strategy optimization. While each sub-problem is solved independently, a precise coordination and feedback mechanism ensures that the solutions to these two sub-problems complement each other to achieve the overall optimal solution. Specifically, bandwidth allocation optimization dynamically adjusts resource allocation by considering the bandwidth resources of each satellite and user needs, while handover strategy optimization adjusts handover decisions based on the current network status and user location to minimize downtime.

[0189] In this 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 magnitude of ξ is first determined. 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. Next, the reduced ξ value is substituted back into the constraint conditions for verification. If the constraint conditions are satisfied, the reduction process is complete. Otherwise, the above operation continues until a switching strategy ξ that meets the constraint requirements is finally obtained.

[0190] During the above process, the system dynamically adjusts its solution strategy based on real-time feedback to adapt to changes in network conditions and user needs. In this way, low-Earth orbit satellite networks can maintain optimal performance in dynamically changing environments, thereby ensuring efficient utilization of network resources and continuous optimization of the user experience.

[0191] Ultimately, by combining the results of bandwidth allocation and handover strategy optimization, the overall performance of the low-Earth orbit satellite network can be significantly improved. By maximizing the average rate of user equipment and minimizing handover interruption time, the system can not only ensure the downlink rate for 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 solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A low-Earth orbit satellite handover method based on a dual-activation protocol stack, characterized in that: The method includes the following steps: S1. Establish a non-terrestrial network in a low-Earth orbit satellite network environment, design a handover architecture based on a dual-activation protocol stack with the optimization objectives of maximizing the average rate of user equipment and minimizing handover interruption latency, and establish the original optimization problem. S2. Establish a multi-stage handover mechanism for low-Earth orbit satellite networks, including at least the status acquisition stage, target satellite selection stage, handover execution stage, and 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. The bandwidth allocation subproblem is solved using the alternating direction multiplier method. S5. The simulated annealing algorithm is used to solve the switching strategy subproblem; S6. The final optimal solution is obtained by combining the solution results of the bandwidth allocation subproblem and the switching strategy subproblem; In step S3, firstly... Relaxation is a continuous variable with a range of Secondly, new variables are introduced. and This represents the positive and negative parts of the slack variables; finally, the optimization problem is reconstructed, decomposed into a bandwidth allocation problem and a switching strategy problem; among them, The slack variable is the time required for the user to connect to the target satellite after making a handover decision. Therefore, the original optimization problem P1 is optimized to P2: By fixing the switching strategy variable and the bandwidth allocation variable respectively, the original problem is decomposed into two independent subproblems for solution. The objective function value is then determined. Defined as , only As free variables, we obtain the bandwidth allocation subproblem: Then, based on the solution to the bandwidth allocation subproblem, the switching strategy subproblem is further obtained: In the formula, As the independent variable of the switching strategy subproblem.

2. The low-Earth orbit satellite handover 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. A time frame structure is designed, with each frame having a length of [missing information]. The interrupt switching latency is... ; Using sets This represents the N satellites in a satellite constellation, a set. Let N be the set of all users, randomly distributed within the coverage area of ​​N satellites. The user set is divided into those supporting a handover strategy based on the dual-activation protocol stack and those using a traditional handover strategy. The set of users supporting the dual-activation protocol stack is... ; Design related indicators Describe the user With satellite During the handover process, the connection status when At that time, it indicates the satellite User The service satellites, with a downlink between them; the target satellite set up To capture the associated transfer status after the switch is completed; use This indicates the switching strategy, and its value is... ,in, Indicates user A dual-activation handover strategy is adopted to switch to the target satellite. ; This indicates that the user should maintain the current connection state and not perform a switch. Indicates user Switch to the target satellite using traditional handover strategies. Interruption delays are allowed; Set at time satellite For users The allocated bandwidth is It satisfies the following bandwidth allocation constraints: In the formula, The maximum bandwidth for 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 follows: in, At the speed of light, The distance between the UE and the satellite. For carrier frequency; Channel vector The channel response from the satellite to the UE, following Rayleigh fading, is a circular symmetric complex Gaussian random variable with zero mean and unit variance. ; Under Rayleigh fading conditions, the signal-to-noise ratio (SNR) and channel gain Relatedly, the formula for calculating SNR is: in Indicates the satellite's transmission power. Noise power; Then we have: In the formula, For users At any moment From satellite The received downlink rate.

3. The low-Earth orbit satellite handover 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 connection with both satellites simultaneously during the handover execution phase. During this phase, the source satellite continues to allocate downlink packet data aggregation protocol layer sequence number (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 downlink PDCP SDUs that do not contain sequence number SN. During the handover execution phase, the downlink data received by the user includes superimposed data from the source satellite and the target satellite, as well as protocol processing data; The amount of data received by the target satellite is expressed as follows: In the formula, This represents the loss factor, used to adjust for the difference between the theoretical maximum data rate and the actual achieved rate; Indicates satellite The load; This indicates the number of users who switched to the target satellite; For data request interval, This is the data request lead time offset, used to request data in advance; Let the amount of data transmitted by the source satellite be expressed as: Target satellite The amount of data sent is: In the formula, Indicates the duration of this phase; Therefore, the total amount of data received by the user is expressed as: Calculate the proportion of data packets: calculate Effective data volume: The downlink rate during the user's handover execution phase is expressed as: Introducing additional latency The received data packets are reordered, and the delay is rearranged. There exists an upper bound, defined as the source satellite. and target satellite The maximum difference between the expected downlink latency of nodes is expressed as: in, Indicates source satellite The expected downlink delay , Indicates user With satellite Downlink interruption probability, Indicates user With satellite Downlink transmission delay Indicates user With satellite Downlink transmission delay via HARQ entity for retransmission; target satellite downlink delay considering inter-satellite link delay. Expected downlink delay of the target satellite Represented as: Indicates user With satellite Downlink interruption probability, Indicates user With satellite Downlink transmission delay Indicates user With satellite Downlink transmission delay when retransmitted via HARQ entity; Connection interruption probability Defined as when the signal-to-noise ratio of user equipment in satellite-to-user transmission is lower than a predetermined threshold. The probability of is expressed as: Define a new variable: but ,in The probability of connection interruption can be further expressed as: downlink delay Primarily determined by propagation delay, under a hybrid automatic repeat request mechanism, if a data packet is retransmitted once, the downlink delay... Represented as ,in Represents the speed of light; The downlink latency of DAPS handover is lower than that of traditional handover strategies, satisfying the following inequality: Right now: in, This is the downlink delay of the traditional handover strategy.

4. The low-Earth orbit satellite handover method based on a dual-activation protocol stack according to claim 3, characterized in that: Based on the established handover architecture using a dual-activation protocol stack, the original optimization problem P1, with the optimization objectives of maximizing the average rate of user equipment and minimizing handover interruption latency, is expressed as: C1.1 represents the user integrating the dual-activation protocol stack. The switching strategy for the first user is as follows: C1.2 specifies that the bandwidth allocation for the service user meets the minimum guarantee requirements; C1.3 and C1.4 specify that each user can only switch to one target satellite at a time, and require that 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 limit the conditions for using the dual-active switching strategy, where 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 of the PDCP layer.

5. A low-Earth orbit satellite handover method based on a dual-activation protocol stack according to claim 4, characterized in that: In step S2, within the established multi-stage switching mechanism of the low-Earth orbit satellite network, the satellite topology remains stable within a single time frame, and the length of each time frame is fixed. Each time frame is divided into the following four stages: Status acquisition phase: Each satellite measures the signal strength of its served 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 its local status information; Handover Execution Phase: Based on the handover decision, the User Equipment (UE) establishes a downlink connection with the target satellite. This phase lasts for [duration missing]. It is 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 continue until the start of the next status acquisition phase. If within a time frame, the satellite The decision regarding the user is based on the measurement results during the target satellite selection phase. 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 this satellite.

6. The low-Earth orbit satellite handover method based on a dual-activation protocol stack according to claim 5, characterized in that: In step S4, the bandwidth allocation sub-problem is addressed in the switching strategy. Under fixed conditions, 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 subproblem involves only one satellite, and the global optimization problem is solved by coordinating local variables.

7. A low-Earth orbit satellite handover method based on a dual-activation protocol stack according to claim 6, characterized in that: In step S5, the switching strategy optimization subproblem is solved using the simulated annealing algorithm. By iteratively adjusting the switching strategy and accepting non-optimal solutions according to a preset probability, the problem avoids getting trapped in local optima and finally finds 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 that of the current solution, the solution is accepted directly; otherwise, a non-optimal solution is accepted based on the control probability of the current temperature. As the algorithm iterates, the temperature gradually decreases, which reduces the probability of accepting a non-optimal solution, thus realizing the exploration of the optimal switching strategy from a global perspective.

8. A low-Earth orbit satellite handover method based on a dual-activation protocol stack according to claim 7, characterized in that: In step S6, the final optimized solution is obtained by solving the bandwidth allocation and handover strategy optimization sub-problems respectively, which maximizes the average rate of the UE and minimizes the handover interruption time. Within each time frame, the system solves the bandwidth allocation and handover strategy optimization sub-problems independently, and establishes a coordination and feedback mechanism between the two. The bandwidth allocation optimization dynamically adjusts resource allocation by considering the bandwidth resources of each satellite and user needs, while the handover strategy optimization adjusts handover decisions based on the current network status and user location to minimize downtime.

9. A low-Earth orbit satellite handover method based on a dual-activation protocol stack according to claim 8, characterized in that: In step S6, based on the solution to the bandwidth allocation and switching strategy optimization problem, a greedy reduction method is used to adjust the slack variables. The restoration process is as follows: First, determine The size, when If the value of is not equal to 0, and it is greater than 0, then it is set to 1; If it is less than 0, then it is taken as -1; Then restore The value is then returned to the constraints for verification. If the constraints are satisfied, the restoration process is complete. Otherwise, continue the above operations until a switching strategy that meets the constraints is finally obtained. .

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