In resource constrained satellite-terrestrial integrated networks (STINs), satellite downlinks supporting earth stations often have to share the same band with terrestrial networks. Under this scenario, achieving secure and timely communication in STINs could be challenging due to the presence of co-channel interference, imperfect CSI, and potential eavesdroppers. Existing security techniques in STINs e.g. robust secure beamforming (BF) often overlook another key performance indicator of STINs, i.e. communication timeliness in terms of Age of Information (AoI). To overcome this issue, this paper proposes a new joint AoI and security-oriented optimization in enhancing the performance of STINs. Specifically, two schemes are developed to achieve low latency and secure BF, including a single-slot scheme and a multi-slot scheme. Specifically, we first establish a continuous-time AoI evolution model and derive a closed-form secrecy margin for the wiretap channel, which enables a unified characterization of information freshness and transmission security. Building on this, we incorporate imperfect channel state information (CSI) to formulate a single-slot joint optimization problem that explicitly targets both AoI-aware freshness and physical-layer security. The objective is to minimize the total transmit power, while meeting the required secrecy-margin constraints, quality of service (QoS) constraints, eavesdropping probability constraints, and pertransmitter power budget constraints. To handle this nonconvex problem, we first apply Bernstein inequalities to convert the probabilistic constraints into deterministic forms. Subsequently, an iterative difference-of-convex programming algorithm is proposed to derive the BF vectors. Furthermore, to capture multi-slot temporal dynamics, we extend the design to a multi-slot framework that considers the impact of random data arrivals on system performance and establishes queue stability conditions based on the data queue. We apply the Lyapunov optimization technique to transform the multi-slot stochastic problem into a per-slot penalized power minimization problem, after which each slot can be solved in the same manner as the single-slot design. Finally, experimental results show that the proposed single-slot scheme satisfies both security and timeliness requirements while significantly reducing system power consumption, whereas the multi-slot optimization retains these performance advantages and further enables a favorable trade-off between power consumption and queue stability.

This paper investigates a semi-grant-free (SGF) access scheme for satellite communication systems, where one earth station (ES) and many mobile terminals (MTs) desire to access the satellite network simultaneously via uplink non-orthogonal multiple access (NOMA). We first propose two NOMA assisted SGF transmission schemes according to the availability of different channel state information (CSI). When perfect CSI is available, the satellite broadcasts an instantaneous access threshold to all MTs to enable dynamic power control (DPC), thus guaranteeing the quality of service of the ES. Otherwise, with the introduction of a statistical access threshold, a novel DPC with probability constraint is proposed to fulfill a satisfactory transmission. Next, we propose a new probability density function to characterize the shadowed-Rician distribution with estimation error, with which closed-form system throughput expressions under the proposed schemes are derived. Finally, computer simulations validate the effectiveness and superiority of our analysis and reveal the impact of CSI errors on the system performance.

This paper investigates a semi-grant-free (SGF) based transmission strategy to provide a flexible connectivity for various kinds of users in an integrated satellite-aerial-terrestrial network (ISATN). Herein, a high-altitude platform (HAP) termed as a grant-based user (GBU), which serves multiple mobile terminals (MTs) through space division multiple access (SDMA), wants to access a satellite network with multiple earth stations (ESs) termed as grant-free users (GFUs) simultaneously via non-orthogonal multiple access (NOMA) assisted SGF. To this end, we first propose two SGF-based uplink transmission schemes for both perfect channel state information (CSI) and imperfect CSI cases. When perfect CSI is available, a zero-forcing based beamforming (BF) scheme is used in HAP network while an adaptive transmit power allocation (ATPA) approach is adopted for SGF transmission. When only imperfect CSI is available, BF scheme employing the derived channel correlation matrix of HAP-MT link is proposed to achieve SDMA, and a novel ATPA strategy with rate probability constraint is proposed to guarantee quality-of-service of the GBU. Next, we derive the closed-form throughput expressions to evaluate the performance of the considered ISATN with the proposed two SGF-based schemes. Finally, computer simulations are conducted to validate the theoretical performance analysis and show the superiority of the proposed schemes over the related works. Moreover, our numerical results not only demonstrate a satisfactory performance of the proposed SGF-based scheme using imperfect CSI, but also reveal the impact of CSI errors on the system performance.

Satellite and unmanned aerial vehicle (UAV) integrated networks (SUINs) are considered as a promising method to offer various Internet of Remote Things (IoRT) applications. In this article, we investigate the downlink transmission of SUINs where the satellite-to-UAV link uses the free-space optical (FSO) technology with an equal gain combining (EGC) scheme while the links from UAV to IoRT devices exploit radio frequency (RF) with the space-division multiple access (SDMA) technique. Specifically, considering that only statistical channel state information (CSI) is available, we first formulate an optimization problem to maximize the ergodic sum rate (ESR) of the system, which is constrained by the total transmit power budget and IoRT devices’ rate requirements. Then, a beamforming (BF) scheme based on the alternating direction method of multipliers (ADMM) is proposed to solve the nonconvex problem. Furthermore, a zero-forcing (ZF)-based suboptimal approach is also presented to reduce the implementation complexity. Finally, by assuming that the FSO link and RF links are subject to Gamma–Gamma fading and Nakagami-$m$fading, respectively, we derive closed-form ESR expressions for the considered network with the proposed BF schemes. Simulation results are provided to confirm the accuracy of the theoretical analysis. Moreover, it is revealed that our proposed EGC scheme for FSO communication and BF schemes for RF transmission can both achieve better performance than the existing works.

In this paper, we propose a joint beamforming (BF) and power allocation scheme for non-orthogonal multiple access based multibeam satellite systems. Unlike the existing works where perfect channel state information (CSI) is required, we use imperfect CSI in formulating a constrained optimization problem aiming to minimize the maximum individual antenna powers subject to the outage constraints of quality-of-service requirements. Since the original problem is mathematically intractable, we first adopt Bernstein-Type II inequality to convert the outage constraints into deterministic forms. Then, an alternating optimization algorithm is proposed to jointly design BF vectors and power allocation coefficients. Finally, simulation results are provided to demonstrate the robustness and superiority of the proposed scheme compared with benchmark schemes.

Integrating non-orthogonal multiple access (NOMA) in intelligent reflecting surface (IRS) is expectedly an effective solution to enhance system's spectrum efficiency. In this paper, we investigate joint beamforming and power allocation for uplink NOMA transmission in an IRS-assisted cognitive satellite and terrestrial network operating at millimeter wave frequency band. Specifically, based only on imperfect channel state information in terms of the angular information of both primary users (PUs) and secondary users, we formulate an optimization problem to maximize the sum rate of the PUs in terrestrial network. To handle the resulting intractable optimization problem, we first transform the uncertainty channel vectors into a deterministic form with the aid of angular discretization. Then, by combining successive convex approximation with Taylor expansion and S-procedure methods, we propose an optimization scheme to jointly optimize the beamforming weight vector and power coefficients. Finally, simulation results show that the proposed scheme can achieve outstanding sum rate performance compared to state-of-the-art schemes.

High-throughput satellites (HTSs) play an important role in future millimeter-wave (mmWave) aeronautical communication to meet high speed and broad bandwidth requirements. This paper investigates the outage performance of an aeronautical broadband satellite communication system’s forward link, where the feeder link from the gateway to the HTS uses free-space optical (FSO) transmission and the user link from the HTS to aircraft operates at the mmWave band. In the user link, spot beam technology is exploited at the HTS and a massive antenna array is deployed at the aircraft. We first present a location-based beamforming (BF) scheme to maximize the expected output signal-to-noise ratio (SNR) of the forward link with the amplify-and-forward (AF) protocol, which turns out to be a phased array. Then, by supposing that the FSO feeder link follows Gamma-Gamma fading whereas the mmWave user link experiences shadowed Rician fading, we take the influence of the phase error into account, and derive the closed-form expression of the outage probability (OP) for the considered system. To gain further insight, a simple asymptotic OP expression at a high SNR is provided to show the diversity order and coding gain. Finally, numerical simulations are conducted to confirm the validity of the theoretical analysis and reveal the effects of phase errors on the system outage performance.