This letter shows the first carrier phase tracking and positioning results with Starlink's low earth orbit (LEO) satellite signals. An adaptive Kalman filter based algorithm for tracking the beat ...carrier phase from the unknown Starlink signals is proposed. Experimental results show carrier phase tracking of six Starlink satellites and a horizontal positioning error of 7.7 m with known receiver altitude.
With numerous ongoing deployments owned by private companies and startups, dense satellite constellations deployed in low Earth orbit (LEO) will play a major role in the near future of wireless ...communications. In addition, the 3rd Generation Partnership Project (3GPP) has ongoing efforts to integrate satellites into 5G and beyond-5G networks. Nevertheless, numerous challenges must be overcome to fully exploit the connectivity capabilities of satellite constellations. These challenges are mainly a consequence of the low capabilities of individual small satellites, along with their high orbital speeds and small coverage due to the low altitude of deployment. In particular, inter-plane inter-satellite links (ISLs), which connect satellites from different orbital planes, are greatly dynamic and may be considerably affected by the Doppler shift. In this paper, we present a framework and the corresponding algorithms for the dynamic establishment of the inter-plane ISLs in LEO constellations. Our results show that the proposed algorithms increase the sum of rates in the constellation 1) by up to 115% with respect to the state-of-the-art benchmark schemes in an interference-free environment and 2) by up to 71% when compared to random resource allocation in a worst-case scenario for interference.
Space-air-ground networks play important roles in both fifth generation (5G) and sixth generation (6G) techniques. Low earth orbit (LEO) satellites and high altitude platforms (HAPs) are key ...components in space-air-ground networks to provide access services for the massive mobile and Internet of Things (IoT) users, especially in remote areas short of ground base station coverage. LEO satellite networks provide global coverage, while HAPs provide terrestrial users with closer, stable massive access service. In this work, we consider the cooperation of LEO satellites and HAPs for the massive access and data backhaul of remote area users. The problem is formulated to maximize the revenue in LEO satellites, which is in the form of mixed integer nonlinear programming. Since finding the optimal solution by exhaustive search is extremely complicated with a large scale of network, we propose a satellite-oriented restricted three-sided matching algorithm to deal with the matching among users, HAPs, and satellites. Furthermore, to tackle the dynamic connections between satellites and HAPs caused by the periodic motion of satellites, we present a two-tier matching algorithm, composed of the Gale-Shapley-based matching algorithm between users and HAPs, and the random path to pairwise-stable matching algorithm between HAPs and satellites. Numerical results show the effectiveness of the proposed algorithms.
Space information networks (SINs) have the potential to overcome the coverage and reliability limitations of cellular networks. As a result, SINs have received considerable attention as an enabling ...technology for sixth-generation (6G) networks to support global connectivity. SINs often employ a large number of low Earth orbit (LEO) satellites which are vulnerable to spoofing attacks. Thus, game theoretic physical layer authentication (PLA) based on Doppler frequency spread (DS) and received power (RP) attributes is proposed to provide effective authentication for these satellites. Hypothesis testing with a threshold is used to distinguish between legitimate and illegitimate (spoofer) satellites. Then, a zero-sum PLA game in which the ground station (GS) chooses the optimal detection threshold (<inline-formula> <tex-math notation="LaTeX">\tau ^{*} </tex-math></inline-formula>) to maximize its utility and a spoofing satellite (<inline-formula> <tex-math notation="LaTeX">s </tex-math></inline-formula>) chooses the optimal attack probability (<inline-formula> <tex-math notation="LaTeX">k^{*} </tex-math></inline-formula>) to maximize its utility. Numerical results are presented to demonstrate the effectiveness of the proposed approach.
This letter unveils the unknown structure of Starlink low Earth orbit (LEO) satellites' orthogonal frequency division multiplexing (OFDM)-like reference signals (RSs). The spectrum of Starlink's ...dowlink signals is presented, and the frame length is estimated. A blind receiver is proposed, which acquires via a sequential generalized likelihood ratio test multiple satellites, estimates their RSs and respective Doppler, and tracks their carrier and code phases. Experimental results are presented showing six tracked Starlink LEO satellites, three of which transmitted pure tones, while the other transmitted OFDM-like signals. The achieved horizontal positioning error with the six satellites was 6.5 m.
The next frontier towards truly ubiquitous connectivity is the use of Low Earth Orbit (LEO) small-satellite constellations to support 5G and Beyond-5G (B5G) networks. Besides enhanced mobile ...broadband (eMBB) and massive machine-type communications (mMTC), LEO constellations can support ultra-reliable communications (URC) with relaxed latency requirements of a few tens of milliseconds. Small-satellite impairments and the use of low orbits pose major challenges to the design and performance of these networks, but also open new innovation opportunities. This paper provides a comprehensive overview of the physical and logical links, along with the essential architectural and technological components that enable the full integration of LEO constellations into 5G and B5G systems. Furthermore, we characterize and compare each physical link category and explore novel techniques to maximize the achievable data rates.
This letter shows the first acquisition, Doppler tracking, and positioning results with Starlink's low Earth orbit satellite signals. A generalized-likelihood-ratio-based test is proposed to acquire ...Starlink's downlink signals. A Kalman-filter-based algorithm for tracking the Doppler frequency from the unknown Starlink signals is developed. Experimental results show Doppler tracking of six Starlink satellites, achieving a horizontal positioning error of 10 m.
Recently, low earth orbit (LEO) satellite-based systems have attracted tremendous attention and various technologies have been developed for payload miniaturization and optical communications. In ...addition, mega-constellation architectures are expected to be deployed with LEO satellites for global broadband networks. In this article, we present a thorough analysis of mega-constellation architecture in terms of a change in the number of visible satellites and antenna steering capability to investigate the impact of increase in the constellation size and adoption of optical intersatellite links. The network architecture is evaluated with respect to satellite antenna steering capability and the satellite visibility considering the very narrow beam divergence of optical communications. We analyze the impact of a change in relative positions among the satellites due to continuous satellite movement in the constellation. The results offer guidelines for designing a novel visibility matrix using a time-varying satellite topology. This could defuse the problem of the conventional studies using fixed visibility matrices. The proposed time-varying visibility matrix achieves better performance than the previous preassigned links in terms of end-to-end link distance and hop count of LEO satellite networks.
In Low Earth Orbit (LEO) mega constellations, there are relevant use cases, such as inference based on satellite imaging, in which a large number of satellites collaboratively train a machine ...learning model without sharing their local datasets. To address this problem, we propose a new set of algorithms based on Federated learning (FL), including a novel asynchronous FL procedure based on FedAvg that exhibits better robustness against heterogeneous scenarios than the state-of-the-art. Extensive numerical evaluations based on MNIST and CIFAR-10 datasets highlight the fast convergence speed and excellent asymptotic test accuracy of the proposed method.
Several massive satellite constellations are currently being deployed to complement evolving terrestrial communication networks. Low Earth orbits (LEO) are selected for these constellations due to ...their relative low latency and reduced path-loss where each satellite dwells for a very short period of time within the user's field-of-view. This inherent nature prompts frequent handovers between the satellites and thus causing an increased signaling overhead and possible service interruptions. This letter lays a tractable approach for characterizing satellites' pass-duration using analytic tools, where it captures the satellites positions as a spherically wrapped homogeneous point process and accordingly derives the statistical distribution of the pass-duration. The letter further compares the presented results with well-designed constellations based on Walker-delta pattern. The obtained mean pass-duration is shown to follow a simple dependency on the altitude and provides a close approximation for practical constellation deployments.
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