This paper investigates the massive access for a satellite-aerial-terrestrial network (SATN), where a high-altitude platform (HAP) is deployed as a relay to assist the uplink transmission from terrestrial user equipment (UE) to satellite. Unlike previous works, we adopt radio frequency (RF) and free space optical for the aerial-terrestrial and satellite-aerial links, respectively. Specifically, by assuming that imperfect angular information (IAI) of each UE is known at the HAP, we develop a space division multiple access (SDMA) scheme to maximize the ergodic sum rate (ESR). To this end, we first exploit the IAI to calculate the analytical expression of channel correlation matrix. Then, by considering the limitation of array freedom, we propose a subspace-based UE grouping and scheduling scheme to cluster all UEs into groups. Next, we present a computationally effective beamforming (BF) scheme for each UE at HAP to efficiently implement SDMA in the RF link. Furthermore, a closed-form expression for the ESR of the SATN is derived to validate the proposed BF and SDMA schemes. Finally, simulation results corroborate the derived theoretical formulas and reveal the impacts of array size, angular estimation error, the number of UEs and scheduling threshold on the system performance.

This paper investigates the uplink space division multiple access in a satellite-aerial-terrestrial network, where multiple users access to satellite with the aid of a unmanned aerial vehicle, and the two hops adopt radio frequency (RF) and free space optical (FSO), respectively. We first formulate an optimization problem to maximize the ergodic sum rate (ESR) of the considered system. Then a statistical channel state information (CSI)-based beamforming (BF) scheme is proposed to solve the non-convex ESR maximization problem. The main advantage of the proposed method is that only statistical CSI is used to obtain BF vectors so that a low implementation complexity can be achieved. Then, by assuming that the RF and FSO links undergo Nakagami-m and Gamma-Gamma fading, respectively, closed-form expression for ESR of the considered system is derived. Simulation results validate the derived expression and confirm the effectiveness of the proposed BF scheme.

In this paper, we investigate energy efficient transmission for a satellite-aerial-terrestrial network (SATN), where a multi-antenna unmanned aerial vehicle (UAV) is employed as a relay to assist the satellite signal delivery. By considering total power constraint (TPC) or per-antenna power constraint (PPC) at the UAV, we first formulate an optimization problem to maximize the energy efficiency of the SATN, which is defined as ratio of the ergodic capacity to the total power consumption for communication at UAV. Then, by jointly exploiting array signal processing with the Dinkelbach's method, two new beamforming (BF) schemes, namely, TPC-BF and PPC-BF are proposed to solve the non-convex energy efficiency maximization problem. The main advantage of our method is that only angular information-based channel state information is used to obtain BF weight vectors so that a low implementation complexity is achieved. Furthermore, by assuming that the satellite-UAV link undergoes correlated Shadowed-Rician fading while the UAV-terminal link experiences correlated Rician fading, closed-form expressions for the statistics of the equivalent output signal-to-noise ratio are derived and, thus energy efficiency for the considered SATN with BF schemes is analytically presented. Finally, simulation results corroborate the derived expressions and confirm the effectiveness of the proposed BF schemes.

In this paper, we investigate the outage performance of a multiuser threshold-based decode-and-forward integrated satellite-terrestrial relay network (ISTRN) with opportunistic user scheduling, where the satellite link and terrestrial links undergo Shadowed-Rician (SR) fading and correlated Rayleigh fading, respectively. First, we propose a new probability density function (PDF) to statistically characterize the square sum of independent and identically distributed SR random variables, which is more accurate and concise than existing expressions. Next, based on the new PDF, we derive an analytical expression of outage probability (OP) of the considered network. Furthermore, the asymptotic OP expression is developed at high signal-to-noise ratio to reveal the achievable diversity order of the considered ISTRN. Finally, computer simulation is conducted to validate the analytical results, and show the impact of various parameters on the outage performance.

This paper addresses the secure transmission problem of an integrated satellite-terrestrial relay networks (ISTRN), where multiple malicious eavesdroppers attempt to overhear the confidential signals from the satellite to a terrestrial user. Here, the relay is employed with multiple antenna and the decode-and-forward protocol is used. By supposing that the perfect instantaneous channel state information (CSI) of satellite-relay link and the statistical CSI of relay-user and relay-eavesdropper links are available at the relay, an optimization problem is first formulated to maximize the secrecy rate of the ISTRN. Then, the secure transmission scheme is designed to solve the optimization problem and obtain the closed-form beamforming weight vector. To further insight the secrecy performance of the proposed scheme, we derive the analytical expressions of the secrecy outage probability (SOP) of the considered ISTRN, where the satellite-relay link undergoes the shadowed-Rician fading, and the links of relay to user as well as eavesdroppers undergo the correlated Rayleigh fading. Finally, numerical results are given to confirm the superiority of the proposed scheme and the validity of the SOP analysis.

This study investigates the secrecy performance of a hybrid satellite‐terrestrial relay network (HSTRN) in the presence of multiple eavesdroppers, where the satellite link undergoes Shadowed‐Rician fading, while the terrestrial link follows Rayleigh fading. The authors suppose the direct link between the satellite and the intended user is unavailable due to heavy shadowing and adopt a multi‐antenna relay using either a decode‐and‐forward (DF) or an amplify‐and‐forward (AF) protocol to assist the transmission. By employing perfect channel state information of each link at the relay, the authors first apply receive maximal ratio combining beamforming (BF) and transmit zero‐forcing BF schemes to obtain the output signal‐to‐noise ratios (SNRs) of the intended user and eavesdroppers. Then, based on the Meijer‐G function and the moment generating function, the authors derive the analytical expressions of the ergodic secrecy rate for the considered HSTRN for both DF and AF protocols. Finally, Monte‐Carlo simulations are conducted to validate the theoretical performance analysis and reveal the effects of certain representative parameters on the system secrecy performance.