Recently, low-orbit satellite networks have gained lots of attention from the society due to their wide coverage, low transmission latency, and storage and computing capacity. Providing seamless connectivity to users in different areas is envisioned as a promising solution, especially in remote areas and for marine communication. However, when jointly used with terrestrial networks composing satellite-terrestrial networks, the satellite moving speed is much faster than the ground terminal, which can cause inconsistent service from a single satellite, and therefore lead to frequent satellite handover. Moreover, due to the dynamic and time slot visibility of satellites, the topology of an intersatellite changes frequently, which results in loops during satellite handover, thereby reducing the utilization of links. To address these problems, we propose a digital twin-assisted storage strategy for satellite-terrestrial networks (INTERLINK), which leverages the digital twins (DTs) to map the satellite networks to virtual space for better communication. Specifically, we first propose a satellite storage-oriented handover scheme to minimize the handover frequency by considering the limited access time and capacity constraints of satellites. Then, a multiobjective optimization problem is formulated to obtain the optimal satellite by genetic algorithm. Finally, considering the timing visibility of the satellite links, a digital twin-assisted intersatellite routing scheme is introduced to improve the quality of data delivery between satellites. Simulation results demonstrate that the proposed INTERLINK can reduce both handover times and average propagation delay compared with its counterparts. Meanwhile, benefitting from integrated DT, both the quality of data delivery and the delay of intersatellite links are considerably improved.

Multibeam satellite systems (MSS) enable transmission flexibility and spatial diversity while efficiently reusing the scarce spectrum resource. However, as spectrum reuses tend to introduce co-channel interference, MSS need to address power allocation and interference management carefully. In this paper, we tackle the joint interference pricing and power allocation problems of MSS by formulating the underlying resource allocation problem as a dynamic game model - the Stackelberg model. In our proposed scheme, a fresh satellite user will be charged according to its interference on the satellite system. MSS can dynamically adjust the interference price in order to make a tradeoff between intercell interference and operating profit. Meanwhile, for the satellite user, an equilibrium power allocation should be ascertained in response to the MSS's pricing. A novel market-based solution is proposed for interference management in MSS by introducing an elastic price mechanism. The Nash equilibrium for interference pricing and its iterative convergence for power allocation have further been proven. Numerical results are provided to evaluate the impact of different prices on the utility functions of both MSS and satellite users.

The convergence of terrestrial and non-terrestrial (e.g., satellite communications) infrastructures has been attracting more and more attention from connectivity stakeholders given the forthcoming future sixth-generation (6G) communication paradigm, thanks to ubiquitous coverage and broadcast/multicast capabilities offered by SatCom. With the advent of promising concepts such as the Internet of Space Things (IoST), the potential for applying edge computing in space has become particularly appealing. In particular, in-orbit computing services are provided employing edge servers placed on satellites, which can inherently offer storage and computation capacity. However, an open problem is to find out onboard which satellite edge servers should be placed and how distributed edge computing services could be offered. In this respect, this paper proposes satellite-terrestrial integrated edge computing networks (STECN), aiming at minimizing the average response latency and average energy consumption by jointly selecting the optimal deployment of servers and services. First, we propose a general network framework for the STECN. Then, we develop a heuristic algorithm based on K-medoids clustering and non-dominated sorting genetic algorithm-II (NSGA-II) to solve the optimization problem. Specifically, we achieve the optimal placement of edge servers by exploiting the K-medoids clustering method. In terms of service deployment, the conducted performance analysis shows that the proposed solutions can approach the Pareto Front using the NSGA-II technique. Finally, the proposed heuristic algorithm is compared with two benchmark algorithms by means of simulations, verifying the effectiveness of our proposed algorithm. To the best of our knowledge, this paper is the first work considering server placement and service deployment in STECN.

Delay/disruption tolerant networking (DTN) was developed to enable automated network communications despite frequent and lengthy link disruptions and long link delay. DTN communications rely heavily on a bundle protocol (BP) that uses the well-known approach of store and forward with optional custody transfer for which a node agrees to hold BP data units, bundles, in memory (or storage) until its successful reception is acknowledged by the next node. However, in the presence of long link disruptions, little work has been done regarding performance modeling of BP for reliable data transfer in deep-space communications. In this paper, we present a study of BP over a relay-based deep-space communications system, characterized by lengthy link disruptions accompanied by an extremely long propagation delay, lossy data links, and asymmetric channel rates. An analytical model is built to estimate the total delivery time of a file (message) that is transmitted as the contents of one or more BP bundles over a deep-space channel. A model is also built to characterize the dynamics of memory occupancy and release when BP is used for reliable data delivery in the presence of link disruptions. The constructed models are validated by running experiments using a test bed.

The performance of delay/disruption tolerant networking (DTN) protocols in cislunar and deep-space communication systems has previously been studied by simulation. However, little work has been seen in characterizing in an analytical manner the performance of DTN protocols for space with respect to asymmetric channel rates. We present a performance characterization of the recently developed DTN Licklider transmission protocol (LTP) convergence layer adapter (CLA) (or simply LTPCL) over cislunar space channels with data-rate asymmetry. Analytical models are built to characterize LTPCL with respect to the minimum number of bundle protocol (BP) bundles that should be aggregated to avoid delay in acknowledgment (ACK) transmission and the optimal number of bundles to be aggregated for the best transmission efficiency of BP/LTPCL, with the effect of full overhead at all layers taken into consideration. The models are validated by file transfer experiments running BP/LTPCL protocols using a PC-based testbed.