Securing the Inter-Spacecraft Links: Doppler Frequency Shift based Physical Layer Key Generation

We propose a novel physical layer secret key generation method for the inter-spacecraft communication links. By exploiting the Doppler frequency shifts of the reciprocal spacecraft links as a unique secrecy source, spacecrafts aim to obtain identical secret keys from their individual observations. We obtain theoretical expressions for the key disagreement rate (KDR). Using generalized Gauss-Laguerre quadrature, we derive closed form expressions for the KDR. Through numerical studies, the tightness of the provided approximations are shown. Both the theoretical and numerical results demonstrate the validity and the practicality of the presented physical layer key generation procedure considering the security of the communication links of spacecrafts

A Stochastic Geometry Approach to Doppler Characterization in a LEO Satellite Network

A Non-terrestrial Network (NTN) comprising Low Earth Orbit (LEO) satellites can enable connectivity to underserved areas, thus complementing existing telecom networks. The high-speed satellite motion poses several challenges at the physical layer such as large Doppler frequency shifts. In this paper, an analytical framework is developed for statistical characterization of Doppler shift in an NTN where LEO satellites provide communication services to terrestrial users. Using tools from stochastic geometry, the users within a cell are grouped into disjoint clusters to limit the differential Doppler across users. Under some simplifying assumptions, the cumulative distribution function (CDF) and the probability density function are derived for the Doppler shift magnitude at a random user within a cluster. The CDFs are also provided for the minimum and the maximum Doppler shift magnitude within a cluster. Leveraging the analytical results, the interplay between key system parameters such as the cluster size and satellite altitude is examined. Numerical results validate the insights obtained from the analysis.Comment: Accepted in IEEE International Conference on Communications (ICC) 202

Architectures and Key Technical Challenges for 5G Systems Incorporating Satellites

Satellite Communication systems are a promising solution to extend and complement terrestrial networks in unserved or under-served areas. This aspect is reflected by recent commercial and standardisation endeavours. In particular, 3GPP recently initiated a Study Item for New Radio-based, i.e., 5G, Non-Terrestrial Networks aimed at deploying satellite systems either as a stand-alone solution or as an integration to terrestrial networks in mobile broadband and machine-type communication scenarios. However, typical satellite channel impairments, as large path losses, delays, and Doppler shifts, pose severe challenges to the realisation of a satellite-based NR network. In this paper, based on the architecture options currently being discussed in the standardisation fora, we discuss and assess the impact of the satellite channel characteristics on the physical and Medium Access Control layers, both in terms of transmitted waveforms and procedures for enhanced Mobile BroadBand (eMBB) and NarrowBand-Internet of Things (NB-IoT) applications. The proposed analysis shows that the main technical challenges are related to the PHY/MAC procedures, in particular Random Access (RA), Timing Advance (TA), and Hybrid Automatic Repeat reQuest (HARQ) and, depending on the considered service and architecture, different solutions are proposed.Comment: Submitted to Transactions on Vehicular Technologies, April 201

Doppler shift compensation strategies for LEO satellite communication systems

Development of signal processing for communication in NGEO systems in order to counteract the high doppler component.Broadband connectivity only covers one third of the earth's surface. LEO satellite communication systems can be a solution to extend and complement terrestrial networks. Nevertheless, mobile ground-terminals receive high Doppler shift over the satellite channel, due the relative motion between the satellite and the mobile terminal. In this project is analysed the Doppler shift over the satellite channel observed by a mobile terminal. The analysis is done implementing a Matlab Orbital simulator transmitting an OFDM signal. Also is proposed a Doppler shift compensation strategy for LEO communications systems with the implementation of an ML Doppler estimator in the OFDM receiver. Several results are presented to evaluate the Doppler observed by the terminals in different positions as well as the BER for different SNR and Doppler shift.La conectividad de banda ancha actualmente sólo cubre un tercio de la superficie terrestre. Los sistemas de comunicación por satélite LEO pueden ser una solución a tener en cuenta para ampliar y complementar las redes terrestres. Sin embargo, los terminales terrestres móviles reciben un cambio de la frecuencia elevado (efecto Doppler) sobre el canal satélite debido a las velocidades de movimiento relativas entre el satélite y el terminal móvil. En este proyecto se estudia el efecto Doppler sobre el canal satélite observado por un terminal móvil. El análisis se hace implementando un simulador Orbital Matlab que transmite una señal OFDM. También se propone una estrategia de compensación Doppler para los sistemas de comunicaciones LEO con la implementación de un estimador Doppler ML en el receptor OFDM. Se presentan varios resultados en términos de Doppler observado por los terminales en diferentes posiciones, así como la BER para diferentes SNR y Doppler recibido por los terminales.La connectivitat de banda ampla actualment només cobreix un terç de la superfície terrestre. Els sistemes de comunicació per satèl·lit LEO poden ser una solució a tenir en compte per ampliar i complementar les xarxes terrestres. No obstant això, els terminals terrestres mòbils reben un canvi de la freqüència elevat sobre el canal satèl·lit a causa de les velocitats de moviment relatives entre el satèl·lit i el terminal mòbil. En aquest projecte s'analitza el efecte Doppler sobre el canal satèl·lit observat per un terminal mòbil. L'anàlisi es fa implementant un simulador Orbital Matlab que transmet un senyal OFDM. També es proposa una estratègia de compensació Doppler per als sistemes de comunicacions LEO amb la implementació d'un estimador Doppler ML en el receptor OFDM. Es presenten diversos resultats en termes de Doppler observat per els terminals en diferents posicions, així com la BER per a diferents SNR i Doppler rebut per els terminals

Role of satellite communications in 5G ecosystem: perspectives and challenges

The next generation of mobile radio communication systems – so-called 5G – will provide some major changes to those generations to date. The ability to cope with huge increases in data traffic at reduced latencies and improved quality of user experience together with a major reduction in energy usage are big challenges. In addition, future systems will need to embody connections to billions of objects – the so-called Internet of Things (IoT) which raises new challenges.Visions of 5G are now available from regions across the world and research is ongoing towards new standards. The consensus is a flatter architecture that adds a dense network of small cells operating in the millimetre wave bands and which are adaptable and software controlled. But what is the place for satellites in such a vision? The chapter examines several potential roles for satellites in 5G including coverage extension, IoT, providing resilience, content caching and multi-cast, and the integrated architecture. Furthermore, the recent advances in satellite communications together with the challenges associated with the use of satellite in the integrated satellite-terrestrial architecture are also discussed

On the Random Access Procedure of NB-IoT Non-Terrestrial Networks

The standardization of the 5G systems has recently entered in an advanced phase, where non-terrestrial networks will be a new key feature in the upcoming releases. Narrowband Internet of Things (NB-IoT) is one of the technologies that will address the massive machine type communication (mMTC) traf- fic of the 5G. To meet the demanding need for global connectivity, satellite communications can provide an essential support to complement and extend the NB-IoT terrestrial infrastructure. However, the presence of the satellite channel comes up with new demands for the NB-IoT procedures. In this paper, we investigate the main challenges introduced by the satellite channel in the NB-IoT random access procedure, while pointing out valuable solutions and research directions to overcome those challenges

Smart Beamforming for Direct Access to 5G-NR User Equipment from LEO Satellite at Ka-Band

Study how spatial diversity can help in massive IoT and develp signal processing access for MIMO beamformingNon-Terrestrial Networks (NTN), in particular LEO Satellite Networks, are expected to play a key role in extending and complementing terrestrial 5G networks in order to provide services to air, sea and un-served or under-served areas. This work proposes the implementation of a novel scheme called Resource Sharing Beamforming Access (RSBA), which seems a promising solution to deal with scenarios where Bit Error Rate (BER), probability of collision and/or achievable rate are important aspects of study. Given the system architecture presented in this work, RSBA will be proposed as solution in the 5G-NR Sat-IoT scenario. As it is expected, a huge amount of IoT devices will be transmitting in the uplink, and being the case of Non-Orthogonal-Multiple-Access (NOMA), the risk of collisions between devices will increase. The idea, after assessing the channel impairments of a direct link between a LEO Satellite and a NB-IoT device, it to study how spatial diversity via smart beamforming at the receiver will reduce the probability of collision between the devices, and thus increasing the number of users that can access to the media

Quasi-Synchronous Random Access for Massive MIMO-Based LEO Satellite Constellations

Low earth orbit (LEO) satellite constellation-enabled communication networks are expected to be an important part of many Internet of Things (IoT) deployments due to their unique advantage of providing seamless global coverage. In this paper, we investigate the random access problem in massive multiple-input multiple-output-based LEO satellite systems, where the multi-satellite cooperative processing mechanism is considered. Specifically, at edge satellite nodes, we conceive a training sequence padded multi-carrier system to overcome the issue of imperfect synchronization, where the training sequence is utilized to detect the devices' activity and estimate their channels. Considering the inherent sparsity of terrestrial-satellite links and the sporadic traffic feature of IoT terminals, we utilize the orthogonal approximate message passing-multiple measurement vector algorithm to estimate the delay coefficients and user terminal activity. To further utilize the structure of the receive array, a two-dimensional estimation of signal parameters via rotational invariance technique is performed for enhancing channel estimation. Finally, at the central server node, we propose a majority voting scheme to enhance activity detection by aggregating backhaul information from multiple satellites. Moreover, multi-satellite cooperative linear data detection and multi-satellite cooperative Bayesian dequantization data detection are proposed to cope with perfect and quantized backhaul, respectively. Simulation results verify the effectiveness of our proposed schemes in terms of channel estimation, activity detection, and data detection for quasi-synchronous random access in satellite systems.Comment: 38 pages, 16 figures. This paper has been accepted by IEEE JSAC SI on 3GPP Technologies: 5G-Advanced and Beyond. Copyright may be transferred without notice, after which this version may no longer be accessibl