Satellite communication systems, particularly those using Low Earth Orbit (LEO) satellites, have gained significant attention due to their low-latency, high-throughput capabilities, and potential to provide global coverage, especially in underserved areas. However, a key challenge in LEO satellite communication is the Doppler shift effect, caused by the relative motion between the satellite and the ground terminal. This phenomenon leads to frequency shifts, which can result in synchronization errors, signal degradation, and communication inefficiencies. While various Doppler shift compensation methods have been proposed, such as coarse compensation using satellite ephemeris data and fine compensation using pilot-assisted estimation, existing solutions still face limitations, particularly in dynamic and high-speed satellite communication environments. In this paper, we propose an innovative two-stage Doppler compensation scheme that combines both coarse compensation based on ephemeris data and fine compensation using pilot-assisted estimation, with a focus on LEO satellite constellations. The key innovation of our approach lies in the integration of adaptive compensation techniques that dynamically adjust based on the relative motion of the satellite constellation and the ground terminal. This enables real-time compensation that not only mitigates Doppler shifts but also improves the quality of service in satellite networks. By addressing the limitations of existing solutions and offering a more flexible, real-time, and adaptive compensation mechanism, simulation results show that our proposed method significantly improves the reliability and throughput of LEO satellite networks, paving the way for more efficient and robust global satellite communication systems.

Integrated satellite-terrestrial networks (ISTNs) are increasingly recognized for their global communication. However, the existing research mainly focuses on simplified ISTNs, where cooperative strategies between satellites and base stations (BSs) are not easily applicable to real-world scenarios. There is a pressing need to investigate more realistic and complex ISTNs to address this gap. To address this gap, we investigate a more realistic and complex ISTN configuration, characterized by a large number of BSs, each divided into interference and service areas. Based on two cooperative modes, i.e., overlay and underlay spectrum sharing, two multiple access schemes are proposed for complex ISTNs using promising rate-splitting technology. These schemes consider multiple constraints simultaneously, such as communication delay, information rate, and power limit. Furthermore, a delay-rate adaptive user grouping strategy is proposed according to communication delay and information rate. For these schemes, the corresponding weighted sum rate problems are formulated, and an improved alternating optimization (AO) method is designed to solve the nonconvex challenges in two spectrum sharing modes. Moreover, a satellite-terrestrial coordinated iteration strategy based on AO is proposed to reduce the computational complexity in underlay spectrum sharing. Simulation outcomes confirm the advantages of our proposed schemes compared to various standard schemes.

Satellite communication technology has rapidly developed to provide global information services, where low-Earth-orbit (LEO) satellites are the most popular due to lower transmission delay and easier deployment compared to geosynchronous-orbit (GEO) satellites. However, LEO satellites provide information services for a short time due to rapid movement relative to the Earth. When there are no visible LEO satellites, communication will be interrupted, and users must frequently detect accessible satellites, which wastes transmission power and decreases communication quality of service (QoS). To provide continuous information services and reduce detection frequency, we propose a GEO and LEO satellite joint service scheme to improve the communication QoS during the handover process between LEO satellites. Considering the access flexibility and spectrum efficiency, we further introduce a rate-splitting multiple access for the proposed multi-orbit satellite joint service scheme. We establish corresponding optimization problems for different communication scenarios using the weighted sum rate and max-min information rate as measurement indicators. To solve these non-convex optimization problems, we propose different alternating optimization algorithms to transform the initial problems into alternating convex problems. The simulation results show that our design handover schemes improve the communication QoS and reduce detection frequency, indirectly improving energy and spectrum efficiency.

The integrated satellite-terrestrial network (ISTN) has attracted much interest due to its global information serviceability. Recently, rate-splitting multiple access (RSMA) has been widely investigated to achieve highly efficient access. Motivated by this, we design the joint RSMA scheme based on spectrum sharing for the downlink ISTN, where part data of terminals are shared by satellite and base station. Furthermore, the max-min rate (MMR) maximization problem is formulated, and an alternating optimization algorithm based on weighted minimum mean square error is introduced to solve the non-convex problem. Simulations show that the joint RSMA scheme has a higher MMR than baseline schemes.

The multibeam satellite system is crucial for the next generation communication, providing seamless and various information services, such as broadcast and unicast messages. However, catering to the burgeoning number of users within limited spectrum resources presents formidable challenges. In response, rate-splitting multiple access (RSMA) has emerged, leveraging non-orthogonal transmission and precoding strategies concurrently. Therefore, we devise the non-orthogonal broadcast and unicast (NOBU) joint transmission framework using RSMA. Furthermore, amalgamating traditional precoding with frequency reuse techniques, we propose a novel centralized frequency reuse strategy, exhibiting commendable performance alongside reduced computational complexity. Furthermore, we maximize the weighted sum rate (WSR) and introduce an improved alternating optimization algorithm, adept at converting intricate non-convex problem into tractable convex counterpart. Simulation outcomes demonstrate that our proposed schemes have significant improvements in WSR performance and are promising for various practical applications.

Multibeam satellite system (MSS) has become the trend because of its ability to provide seamless information services. However, co-frequency interference between beams significantly deteriorates communication performance. Existing interference management schemes regard MSS as multi-antenna systems and introduce precoding technology to eliminate interference, ignoring the characteristics of beam gain and the limited computing resources of satellites. Motivated by this, we design an adaptive grouping access scheme based on the promising ratesplitting multiple access to mitigate inter-beam interference. We initiate our discussion by formulating the weighted sum rate (WSR) maximization problems and deploying an enhanced alternating optimization strategy to navigate through these intricate non-convex issues. The efficacy and reduced complexity of our suggested approach are validated through simulation outcomes.

Multibeam satellite system (MSS) plays an increasingly important role in the future communication system because of the ability to provide seamless information services. However, multibeam technology will cause serious inter-beam co-frequency interference (IBCFI), significantly deteriorating communication performance. Existing IBCFI management schemes mainly depend on precoding technologies, which regard MSS as multi-antenna systems and ignore characteristics of satellite beam gain and the limited computational resources. Meanwhile, terrestrial channels tend to be independent while satellite channels have a high correlation, which is rarely considered by existing work. On the other hand, rate-splitting multiple access (RSMA) has recently emerged due to the advantages of flexible multiple access and robust interference management. Therefore, we design a two-step adaptive grouping access scheme based on the promising RSMA to handle these challenges, where the first step takes the characteristics of satellite beam gain and computational resources into consideration, and the second step optimizes the channel correlation. Building on the two-step adaptive grouping access scheme, we formulate different weighted sum rate (WSR) maximization problems for different user groups. Furthermore, we introduce an improved alternating optimization algorithm to solve these non-convex problems. Finally, simulation results verify the effectiveness of our proposed scheme in WSR and computational complexity.

To provide seamless communication service, the integrated satellite-terrestrial network (ISTN) has attracted lots of interest, where the promising dynamic spectrum sharing technology is widely used to improve spectrum efficiency. Meanwhile, rate-splitting multiple access (RSMA) has recently emerged due to the advantages of flexible multiple access and robust interference management. Based on the two promising technologies, we design joint satellite-terrestrial RSMA schemes in overlay and underlay spectrum sharing modes for ISTN, which considers both cases with and without inter-beam interference. Furthermore, we propose two adaptive RSMA schemes based on the hybrid spectrum sharing mode for adapting dynamic ISTN, where the number of terminals and spectrum resources available to satellite are unevenly distributed and time-varying due to the broad communication coverage. Finally, we consider the quality of service rate requirements and formulate joint optimization problems to maximize the weighted sum rate. To solve these non-convex optimization problems, we introduce an improved alternating optimization algorithm based on weighted minimum mean square error. Simulation results verify that the proposed schemes have significant performance gains compared with SDMA and NOMA schemes and can better adapt to the dynamic changes in the number of terminals and spectrum resources.

To provide seamless communication service, the integrated satellite-terrestrial network (ISTN) has become the trend of communication development, where terrestrial terminals and satellite terminals share the same spectrum resources. Meanwhile, rate-splitting multiple access (RSMA) has recently emerged for flexible multiple access and robust interference management. Based on the two promising technologies, spectrum sharing and RSMA, we design two coordinated multiple access schemes in overlay and underlay spectrum sharing modes for ISTN. Furthermore, we consider the quality of service rate requirements and formulate joint optimization problems to maximize the weighted sum rate. To solve the non-convex optimization problems, an improved alternating optimization algorithm based on weighted minimum mean square error is proposed. Simulation results verify that the proposed schemes have significant performance gains compared with various baseline schemes.

With the rapid development of communication, the future Internet of Things will greatly expand its coverage to form the space–air–ground–ocean-integrated network (SAGOI-Net) and provide globally ubiquitous applications and services. In SAGOI-Net, the existing research work focused on system design and neglected the theoretical analysis of system performance. Furthermore, the Nakagami-$m$fading model can fit the experimental data better than the Rayleigh and Rice fading models. Also, the Nakagami-$m$fading model can adapt to the SAGOI-Net environment by changing the value of the shaping parameter$m$. However, there is no work to analyze the performance of SAGOI-Net using Nakatomi-$m$fading. Therefore, in this article, the synchronous downlink system is theoretically analyzed using the Nakagami-$m$fading model. However, Then, the statistical characteristics of multiple access interference (MAI) and MAI-plus noise are theoretically derived. Furthermore, the accurate expression of the bit-error rate (BER) for the fading model is also derived. After that, we establish the relationship between the number of users, BER, and the information transmission rate to optimize energy efficiency. Finally, simulation results verify that the theoretical derivation results are reliable and effective.

MIMO system makes full use of the space dimension, in the era of increasingly tense spectrum resources, which greatly improves the spectrum efficiency and is one of the future communication support technologies. At the same time, considering the high cost of direct communication between the two parties in a long distance, the relay communication mode has been paid more and more attention. In relay communication network, each node connected by relay has different security levels. In order to forward the information of all nodes, the relay node has the lowest security permission level. Therefore, it is meaningful to study the physical layer security problem in MIMO two-way relay system with relay as the eavesdropper. In view of the above situation, this paper proposes the physical layer security model of MIMO two-way relay cooperative communication network, designs a communication matching grouping algorithm with low complexity and a two-step carrier allocation optimization algorithm, which improves the total security capacity of the system. At the same time, theoretical analysis and simulation verify the effectiveness of the proposed algorithm.