International Journal of Satellite Communications and Networking最新文献

The Automated Identification System (AIS) was originally developed as a terrestrial system tracking vessels near the coastline. Dedicated channels were allocated within the spectrum historically reserved for maritime applications in the very high frequency (VHF) band, enabling long range communications, up to a few kilometers. There have been various initiatives in the last decade that extended this system with a space segment, enabling global monitoring of vessels beyond the range of terrestrial stations. Recently, the World Radiocommunication Conference has allocated frequencies for the extension of this system to a two-way VHF Data Exchange System (VDES) via satellite. This requires to adapt spaceborne antenna solutions previously developed for AIS, particularly for missions using small satellites and CubeSats. This paper provides a timely review of existing VHF antenna solutions and new concepts under development which could be applicable to VDES missions. Some key metrics are identified to provide a comparative study between various candidate solutions. Considering the range of possible missions, from secondary payloads on-board larger satellites to dedicated constellations, it is believed that a number of antenna products can find application in future VDES space-based infrastructure.

With the expansion in Global Navigation Satellite System (GNSS) constellations and emerging applications utilizing GNSS systems, the issue of detection of interference is evolving as a growing concern in the satellite navigation user community. Threats for GNSS users can be classified as unintentional interference, jamming, and spoofing. Spoofing is more harmful among them because the target receiver might not be aware of the attack and, as a consequence, generate misleading position information. Spoofing attacks are classified as simplistic, intermediate, and sophisticated depending on their complexity of implementation. We focused primarily on the detection of intermediate spoofing attacks by measuring shape distortion (SD) through multiple correlators that cover multiple chips around the prompt tracking point. The SD metric compares the measured and typical values of the autocorrelation function and decides on the spoofing using a noise variance based threshold. The proposed SD metric is found to be very effective in detecting the spoofing attack during the pull-off phase of the attack. The method is verified through simulations, synthetic spoofing data, and the TEXBAT data shared by the University of Texas, Austin. Different formulations of the proposed method are compared to provide an optimal number of correlator taps in each channel.

In the near future, very high throughput satellite (VHTS) systems are expected to have a high increase in traffic demand. However, this increase will not be uniform over the service area and will be also dynamic. A solution to this problem is given by flexible payload architectures; however, they require that resource management is performed autonomously and with low latency. In this paper, we propose the use of supervised machine learning, in particular a classification algorithm using a neural network, to manage the resources available in flexible payload architectures. Use cases are presented to demonstrate the effectiveness of the proposed approach, and a discussion is made on all the challenges that are presented.

This paper aims to investigate the potential advantages and also the limits of source routing when applied to delay-/disruption-tolerant networking (DTN) space networks. To this end, it uses a variant of contact graph routing (CGR) called moderate source routing (MSR), recently proposed by the authors and fully compatible with interplanetary overlay network (ION), the DTN suite developed by NASA-JPL. MSR differs from standard CGR as the route to destination is not recalculated from scratch at each node, but possibly reused, if still valid, by next nodes. For this purpose, the route is saved in a dedicated extension block of the forwarded bundle (the data unit of the bundle protocol, used in DTN). Performance of MSR versus CGR is assessed by considering a simple but very challenging space layout. Numerical results, obtained on a GNU/Linux testbed, show that MSR is effective at reducing the chances of loops, in particular when the source has full knowledge of the state of the network; otherwise, network instabilities are still possible. In this case, they can be neutralized by means of the combined use of source routing and anti-loop tools, as shown in the paper. A further advantage of MSR is that it is compatible with standard CGR, which would facilitate a gradual or partial deployment.

Reinforcement learning (RL) is being considered for future SATCOM systems due to its inherent capability to self-learn the optimum decision-making policy under different scenarios. This capability enables SATCOM systems to manage their resources judiciously and mitigate jamming attacks autonomously without prior jammer type classification. We propose a novel smart reactive SATCOM jamming approach that would not only counter these RL based anti-jamming strategies but would also be effective against conventional anti-jamming schemes, that is, FHSS and DSSS. The proposed jamming approach exploits the limitations in learning patterns of Q-learning-based RL agent and achieves effective jamming while conserving considerable amount of jamming power. To achieve this, we propose an intelligent jamming engine (IJE) along with few potent jamming algorithms and evaluate their performance in terms of throughput degradation of victim SATCOM link, jamming power conservation, and design complexity of the jammer. Software simulations successfully demonstrate the effectiveness of our proposed smart reactive jamming approach which outperforms the standard reactive jammer against RL-based antijamming schemes.

Communication through satellite is of great task and importance especially in the world of telecommunication infrastructure. It plays a leading role for future communication systems. However, the performance of the satellite communication system is dominated by the channel conditions overwhelmed by multipath fading and ionospheric scintillation effects. Maximum ratio combining (MRC) previously used to tackle this problem is characterized with hardware complexity resulted in long processing time, while threshold combining (TC) with simple hardware display poor performance. Thus, evaluation of hybrid TC-MRC, with closed-form expression over composite Rayleigh and Rician fading channel is necessary. In this paper, TC and MRC are combined to improve the signal quality and performance. The data are modulated using M-ary quadrature amplitude modulation and transmitted over the combined effects. The received signals at varying paths are scanned to select the best paths. A mathematical expression using the probability density function of composite Rayleigh and Rician fading channel for mean integrated square error (MISE) is derived. The model is efficiently simulated and the performance is estimated. The results show that the hybrid TC-MRC model achieves lower MISE and processing time compared to threshold combiner and even maximum ratio combiner, and thereby enhance the performance of the satellite communication system.

Satellite communication is one of the essential communication mechanisms that can be used for significant distance and under circumstances where the other communication mechanisms cannot work. Therefore, the security of this communication method is highly needed. Because in this era where information plays an important role, information security becomes the first priority for everyone. When we talk about information security, the key exchange and authentication are two key factors of information security. Whitfield Diffie and Martin Hellman¹ proposed the first key exchange protocol. In the last two or three decades, various authentication schemes have been proposed to create a secure network that mainly depends on classical number–theoretical hard assumptions (factorization or discrete logarithm), but due to the Shor's² algorithm, above-mentioned scheme is no longer secure because any discrete logarithm or factorization problems can be solved by Shor's algorithm in polynomial time if the quantum computer becomes the reality soon. As far as our knowledge goes, there is no authentication protocol for satellite communication, which is secure against quantum computer attacks. Therefore, in this paper, we first proposed authentication protocol for satellite communication based on ring learning with error which is secure against quantum attacks.