3.1. System Model
The proposed satellite network comprises three primary components: satellite nodes, ground stations, and user terminals. Each satellite node i is characterized by its resource vector , where denotes the computational capacity, represents the available bandwidth, and signifies the storage capacity.
The network topology is encapsulated by the adjacency matrix , where each element defines the connection attributes between satellite nodes i and j. Specifically, denotes the bandwidth and denotes the latency between node i and node j, respectively.
The satellite network employs a SDN controller to enable centralized management and dynamic resource scheduling. Acting as the global coordination center, the SDN controller continuously monitors the resource status of satellite nodes—including the computing capacity
, bandwidth
, and storage
—as well as link parameters such as transmission delay
and bandwidth
, along with task queue information. Its core functions encompass dynamic domain clustering, multi-path optimization, and resource reallocation. Specifically, each satellite node periodically reports its local resource utilization, link reliability
(Equation (
32)), and task execution status to the SDN controller via dedicated control channels. The controller aggregates this global information and updates the real-time network topology graph
. Based on the current network state, the controller performs dynamic domain clustering by optimizing the utility function
as defined in Equation (
30), determining the affiliation of nodes to logical domains
. The clustering process minimizes the weighted objective
to balance intra-domain link reliability and overall network overhead, ensuring proximity-based cooperation among nodes, while reducing signaling costs. Subsequently, for each task
j, the controller dynamically selects the optimal path
from the available path set
based on real-time link conditions and node workloads, considering the path reliability (Equation (
33)). The path assignment is then disseminated to the corresponding satellite nodes through the binary variable
(Equation (
2)). During task execution, if a resource overload (
) or link failures are detected, the controller triggers Nash bargaining models (Algorithm 1) and Lagrangian optimization (Algorithm 2) to adjust the resource allocation
and update the task matrix
T, ensuring all system constraints (Equations (
3)–(
9)) are satisfied. Through this mechanism, the SDN controller achieves real-time adaptation of the network topology and efficient resource scheduling, significantly enhancing the robustness and task execution efficiency of the satellite network in dynamic environments.
Data transmission initiates from user terminals, traverses through ground stations, and culminates in task requests directed to the satellite nodes. Task allocation is modeled by the matrix
, where
represents the quantity of resources allocated to task
j by satellite node
i. To ensure the physical realizability of resource allocation variables, this paper imposes the non-negativity assumption:
A multi-path scheduling strategy facilitates parallel data transmission across multiple pathways, mitigating packet loss and reducing latency. Formally, for each task j, a possible path represents a potential transmission route that can be used to transmit data from the source to the destination in the network. The set consists of all such feasible paths that can support the transmission of task j’s data under the current network conditions. Here, k denotes the path index within the set . Each path is characterized by various network parameters, including but not limited to bandwidth, latency, and network load. These parameters are critical in determining the suitability of a path for transmitting the task data.
The number of available paths for task
j is denoted by
k, and the selection of specific paths is modeled using binary variables
. The binary variable
is defined as
where
represents a potential transmission route that can be used to transmit data from the source to the destination in the network.
Thus, the set of possible paths encompasses all paths that meet the network’s resource requirements (e.g., available bandwidth, latency tolerance, etc.) and are considered viable for transmission at any given time. The multi-path scheduling strategy utilizes these possible paths to dynamically allocate transmission tasks across multiple routes, helping to mitigate issues such as packet loss, congestion, and latency, thereby improving the overall network efficiency.
Resource allocation and scheduling are thus formulated as an optimization problem that assigns tasks to paths, while considering resource constraints and network performance metrics.
Resource competition among satellite nodes is modeled using game-theoretic principles. Each satellite node i possesses a utility function that depends on its resource allocation strategy and its interactions with other nodes. The objective for each node is to determine the optimal strategy that maximizes , leading to a game equilibrium (e.g., Nash equilibrium) that guides an equitable and efficient resource distribution. This equilibrium ensures optimal resource utilization and load balancing across the network.
Formally, for each satellite node i, the resource vector is , and the resource demand for each task j is . Task j necessitates data transmission through the network, with path selection governed by the multi-path scheduling strategy. Due to the inherent dynamics in network topology and traffic loads, resource allocation strategies must be adaptable in real time, to optimize network utility.
3.3. Problem Formulation and Objective Function
This section formulates the resource allocation and task scheduling problem as a multi-objective optimization problem in satellite networks. The goal is to maximize the total resource allocation of tasks across satellite nodes to enhance the network throughput, ensuring efficient data transmission within the network; simultaneously, by optimizing resource allocation and path selection, minimize task transmission latency to ensure timely completion of tasks; and reduce computational complexity by controlling the extent of resource adjustments, avoiding excessive computational burdens, and thereby improving system responsiveness, stability, and real-time performance. The following explains each part of the objective function and the meaning of the variables.
Network throughput represents the total amount of data successfully transmitted within the network, which depends on the resources allocated to each task at each satellite node. Let denote the resources allocated to task j at satellite node i. The network throughput is expressed as , where n is the number of satellite nodes, and m is the number of tasks. By maximizing this sum, the optimization goal is to increase the total data transmission, thereby improving the network throughput.
Computational complexity measures the computational load during the resource allocation process. Frequent adjustments in resource allocation lead to a higher computational complexity. This is quantified by the difference between the original resource allocation and the adjusted allocation , expressed as . The total transmission latency D for all tasks should be minimized, where represents the transmission latency for task j. The total latency can be formulated as .
The optimization problem aims to maximize network throughput, while minimizing both computational complexity and transmission latency. This is achieved by optimizing resource allocation and task scheduling to enhance the overall transmission capacity, reduce the computational load, and ensure timely task completion. The objective function is formulated as
s.t.
where
,
, and
are weighting factors balancing the importance of throughput, latency, and computational complexity, respectively.
represents all combinations of resource allocation, task scheduling, and path selection that satisfy the constraints.
Specifically, the definition of
is
Here, represents the task–resource allocation matrix, represents the resource constraints at each satellite node, and represents the transmission path for each task.
For the variables in the objective function, represents the amount of resources allocated to task j at satellite node i. By maximizing the sum of resource allocations for all tasks at all nodes, i.e., , we aim to increase the overall throughput of the network (i.e., the total amount of data transmitted). The term quantifies the computational complexity due to resource allocation adjustments, while represents the total transmission latency across all tasks.
Theorem 1. The problem defined in Equation (
10)
is NP-hard. Proof. We prove that the proposed optimization problem is NP-hard by reducing a well-known NP-hard problem, the Multipath Shortest Path Problem (MSPP), to our resource allocation and task scheduling problem.
The MSPP seeks to find
k disjoint paths
from source
s to target
t in a given directed graph
, minimizing the total cost, defined as
where
represents the cost associated with each edge
in path
. The total cost is the sum of individual edge costs over all selected paths.
The optimization problem for the MSPP can then be formulated as
To demonstrate that our resource allocation and task scheduling problem is at least as hard as the MSPP, we map each path cost in the MSPP to the resource allocation cost in our model. We define the resource allocation decision variable
for task
j at node
i and introduce a cost function for resource utilization:
where
represents the cost of assigning resources at node
i for task
j. This function directly parallels the MSPP cost function, establishing an equivalence.
Since the MSPP is known to be NP-hard, and our problem generalizes the MSPP by introducing resource allocation dependencies, our problem is at least NP-hard. □