In recent years, as giant satellite constellations grow rapidly worldwide, the co-existence between constellations has been widely concerned. In this paper, we overview the co-frequency interference (CFI) among the giant non-geostationary orbit (NGSO) constellations. Specifically, we first summarize the CFI scenario and evaluation index among different NGSO constellations. Based on statistics about NGSO constellation plans, we analyse the challenges in mitigation and analysis of CFI. Next, the CFI calculation methods and research progress are systematically sorted out from the aspects of interference risk analysis framework, numerical calculation and link construction. Then, the feasibility of interference mitigation technologies based on space, frequency domain isolation, power control, and interference alignment mitigation in the NGSO mega-constellation CFI scenario are further sorted out. Finally, we present promising directions for future research in CFI analysis and CFI avoidance.
In order to achieve dependable and efficient data acquisition and transmission in the Internet of Remote Things (IoRT), we investigate the optimization scheme of IoRT data acquisition under the unmanned aerial vehicle (UAV)-low earth orbit (LEO) satellite integrated space-air-ground network, in which the UAV acquires data from massive Internet of Things (IoT) devices in special scenarios. To combine with the actual scenario, we consider two different data types, that is, delay-sensitive data and delay-tolerant data, the transmission mode is accordingly divided into two types. For delay-sensitive data, the data will be transmitted via the LEO satellite relay to the data center (DC) in real-time. For delay-tolerant data, the UAV will store and carry the data until the acquisition is completed, and then return to DC. Due to non-convexity and complexity of the formulated problem, a multi-dimensional optimization Rate Demand based Joint Optimization (RDJO) algorithm is proposed. The algorithm first uses successive convex approximation (SCA) technology to solve the non-convexity, and then based on the block coordinate descent (BCD) method, the data acquisition efficiency is maximized by jointly optimizing UAV deployment, the bandwidth allocation of IoRT devices, and the transmission power of the UAV. Finally, the proposed RDJO algorithm is compared with the conventional algorithms. Simulation consequences demonstrate that the efficiency of IoRT data acquisition can be greatly improved by multi-parameter optimization of the bandwidth allocation, UAV deployment and the transmission power.
The numbers of beam positions (BPs) and time slots for beam hopping (BH) dominate the latency of LEO satellite communications. Aiming at minimizing the number of BPs subject to a predefined requirement on the radius of BP, a low-complexity user density-based BP design scheme is proposed, where the original problem is decomposed into two subproblems, with the first one to find the sparsest user and the second one to determine the corresponding best BP. In particular, for the second subproblem, a user selection and smallest BP radius algorithm is proposed, where the nearby users are sequentially selected until the constraint of the given BP radius is no longer satisfied. These two subproblems are iteratively solved until all the users are selected. To further reduce the BP radius, a duplicated user removal algorithm is proposed to decrease the number of the users covered by two or more BPs. Aiming at minimizing the number of time slots subject to the no co-channel interference (CCI) constraint and the traffic demand constraint, a low-complexity CCI-free BH design scheme is proposed, where the BPs having difficulty in satisfying the constraints are considered to be illuminated in priory. Simulation results verify the effectiveness of the proposed schemes.
The ultra-dense low earth orbit (LEO) integrated satellite-terrestrial networks (UDLEO-ISTN) can bring lots of benefits in terms of wide coverage, high capacity, and strong robustness. Meanwhile, the broadcasting and open natures of satellite links also reveal many challenges for transmission security protection, especially for eavesdropping defence. How to efficiently take advantage of the LEO satellite's density and ensure the secure communication by leveraging physical layer security with the cooperation of jammers deserves further investigation. To our knowledge, using satellites as jammers in UDLEO-ISTN is still a new problem since existing works mainly focused on this issue only from the aspect of terrestrial networks. To this end, we study in this paper the cooperative secrecy communication problem in UDLEO-ISTN by utilizing several satellites to send jamming signal to the eavesdroppers. An iterative scheme is proposed as our solution to maximize the system secrecy energy efficiency (SEE) via jointly optimizing transmit power allocation and user association. Extensive experiment results verify that our designed optimization scheme can significantly enhance the system SEE and achieve the optimal power allocation and user association strategies.
The gradual deployment of Low-Earth Orbit (LEO) mega constellations with inter-satellite links (ISLs) promises ubiquitous, low-latency, and high-throughput satellite network services. However, networked LEO satellites with ISLs are also at risk of routing attacks such as hijacking. Existing defenses against route hijacking in terrestrial networks can hardly work for the LEO satellite network due to its high spatiotemporal dynamics. To deal with it, we propose RPD, a high-risk routing path detection method for LEO mega-constellation networks. RPD detects abnormal high-risk LEO network paths by checking the consistency between the path delay and the geographical distance. This is efficiently achieved by combining in-band measurements and out-of-band statistical processing to detect the anomaly of the clustering feature in the reference delay matrix. RPD avoids the recalculation of the header cryptographic marks when the handover occurs, thus greatly reducing the cost and improving the performance of high-risk path detection. Experiments showed that the proposed RPD mechanism achieves an average detection accuracy of 91.64% under normal network conditions, and maintain about 89% even when congestion occurs in multiple areas of the network and measurement noise is considered. In addition, RPD does not require any cryptographic operation on the intermediate node, only minimal communication cost with excellent scalability and deployability.
Routing algorithms in satellite constellation networks usually make use of the local state information to adapt to the topology and traffic dynamics, since it’s difficult to obtain the global states in time due to the spatial large-scale feature of constellation networks. Furthermore, they use different range of local states and give these states distinct weights. However, the behind design criterion is ambiguous and often based on experience. This paper discusses the problem from the perspective of complex network. A universal local-state routing model with tunable parameters is presented to generalize the common characteristics of local-state routing algorithms for satellite constellation networks. Based on this, the impacts of local-state routing algorithms on performance and the correlation between routing and traffic dynamics are analyzed in detail. Among them, the tunable parameters, the congestion propagation process, the critical packet sending rate, and the network robustness are discussed respectively. Experimental results show that routing algorithms can achieve a satisfactory performance by maintaining a limited state awareness capability and obtaining the states in a range below the average path length. This provides a valuable design basis for routing algorithms in satellite constellation networks.
With the development of satellite communication, in order to solve the problems of shortage of on-board resources and refinement of delay requirements to improve the communication performance of satellite optical networks, this paper proposes a bee colony optimization algorithm for routing and wavelength assignment based on directional guidance (D-BCO-RWA) in satellite optical networks. In D-BCO-RWA, directional guidance based on relative position and link load is defined, and then the link cost function in the path search stage is established based on the directional guidance factor. Finally, feasible solutions are expanded in the global optimization stage. The wavelength utilization, communication success probability, blocking rate, communication hops and convergence characteristic are simulated. The results show that the performance of the proposed algorithm is improved compared with existing algorithms.
The main geolocation technology currently used in COSPAS-SARSAT system is TDOA/FDOA or three-star TDOA, the principle is to determine the location of the signal source by using the difference in arrival time and frequency of the wireless signal between different receivers. Therefore, ground monitoring stations need to be equipped with more than two antenna receiving stations, and multiple satellites should be able to simultaneously relay the distress signal from the target source in order to achieve the geolocation function. However, when the ground receiving system has only one antenna receiving station, or the target source is in a heavily obscured environment, the ground side is unable to receive the forwarded signals from multiple satellites at the same time, which will make it impossible to locate. To address these problems, in this paper, a time-sharing single satellite geolocations method based on different orbits is proposed for the first time. This method uses one or several low-earth orbit satellites (LEO) and medium-earth orbit satellites (MEO) in the visible area, and the receiving station only needs one pair of receiving antennas to complete the positioning. It can effectively compensate for the shortcomings of the traditional TDOA using the same moment and have better positioning accuracy compared with the single satellite in the same orbit. Due to the limited experimental conditions, this paper tests the navigation satellite using different orbit time-sharing single satellite geolocations, and proves that the positioning method has high positioning accuracy and has certain promotion and application value.
Extensive research attentions have been devoted to studying cooperative cognitive radio networks (CCRNs), where secondary users (SU) providing cooperative transmissions can be permitted by primary users (PU) to use spectrum. In order to maximize SU’s utility, SU may transmit its own information during the period of cooperative transmission, which stimulates the use of covert transmission against PU’s monitoring. For this sake, this article reviews the motivations of studying covert communications in CCRN. In particular, three intelligent covert transmission approaches are developed for maximizing SU’s utility in CCRNs, namely, intelligent parasitic covert transmission (IPCT), intelligent jammer aided covert transmission (IJCT) and intelligent reflecting surface assisted covert transmission (IRSC). Further, some raw performance evaluations are discussed, and a range of potential research directions are also provided.
