LAUSR

Driven by the massively growing applications in Internet of Things (IoT) and the new requirements of the six-generation (6G) wireless network, the amount of terrestrial mobile devices (TMDs) and data traffic in wireless communications have increased explosively. Consequently, the integrated terrestrial-satellite relay networks (ITSRNs) have emerged to address the issue of the huge wireless traffic with the limited allocated resources, which attracts extensive research attention to the field of IoT. However, previous research works in ITSRN mostly focus on terrestrial relays (TRs) configured on the ground, which can only perform limited improvement to the networks on system throughput. In this paper, by introducing an aerial relay (AR), we propose a novel structure of ITSRN and investigate the system throughput maximization and energy consumption minimization problems by jointly optimizing power allocation and AR altitude. In this system, the system implementation includes two periods: satellite to relay (S-R) period and satellite to devices (S-D) period. To maximize the overall system throughput, we propose a joint optimization scheme of the power allocation and altitude of AR. Specifically, due to the non-convexity of the original formulated problem, a bilevel programming method is proposed to obtain the global optimal solution, where the closed-form expressions of power allocation and the optimal altitude of AR are derived to reduce the complexity of the proposed scheme. Subsequently, we investigate the energy consumption minimization problem during S-R period, which is formulated as a convex problem. To achieve the minimum energy consumption, we propose a low complexity algorithm and derive the optimal closed-form solution based on the rigorous mathematical analysis. The effectiveness of the proposed algorithms and solutions are verified by extensive simulations.