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A current trend in the evolution of mobile communication networks consists in integrating Non-Terrestrial Networks (NTN) with the Terrestrial ones. One option to implement the NTN part of this hybrid architecture using Unmanned Aerial Vehicles (UAV) that relay the uplink radio signals through optical wireless backhaul links. A good choice for the radio uplink waveform is conventional SC-FDMA, which mitigates the PAPR and enables a longer battery lifetime at the transmitter side. For the optical backhaul link, which is based on low-cost Visible Light Communication (VLC) technology, a non-orthogonal implementation of SC-FDMA is proposed. By doing so, it is possible to improve the end-to-end throughput by reducing the communication bandwidth (to make it fit the LED frequency response), mitigate the effect of light reflections, and increase the energy efficiency in the backhaul link. Since VLC relies on non-coherent IM/DD, the non-orthogonal SC-FDMA waveform must rotate the phase of the IDFT subcarriers, in order to obtain real-valued signal samples at the output. Two strategies for relaying the data in the UAV node are evaluated, namely: Detect-and-Forward and Decode-and-Forward. The first one recovers the modulation part (i.e. partial regeneration), whereas the second one regenerates the transmitted message up to the bit level (i.e., total regeneration). This paper studies the combination of relaying strategy and NB-IoT Modulation and Coding Scheme (MCS) that maximizes the end-to-end throughput at different UAV altitudes. ; Grant numbers : TERESA - Hybrid TERrEstrial/Satellite Air Interface for 5G and Beyond (TEC2017-90093-C3-1-R) and from the Catalan Government under grants 2017-SGR-891 and 2017-SGR-1479 projects.

This paper studies the data rate that a High Throughput Satellite (HTS) system with fully-regenerative payload can achieve when using an intensity modulation/direct detection optical feeder link. A low-order M-ary Pulse Amplitude Modulation (M-PAM) with time-packing is used to modulate the intensity of the laser diode beam, making use of an external Mach-Zehnder modulator. These M-PAM symbols are recovered on-board the satellite with the aid of a photodetector, and are then encapsulated into the 5G radio frame of the access link. The M-PAM modulation order and the overlapping factor of timepacking are jointly selected to tackle the impact of slowly-varying weather conditions. Moreover, the inter-symbol interference that time-packing introduces is mitigated in reception using a Viterbi equalizer. As expected, time-packing enables a finer granularity on the link adaptation capability of the optical feeder link, enabling to adjust its spectral efficiency according to the moderate attenuation that thin cloud layers introduce. ; Grant numbers : This work has received funding from the Ministry of Science, Innovation and Universities of Spain under project TERESA-TEC2017-90093-C3-1-R (AEI/FEDER,UE) and from the Catalan Government under Grants 2017-SGR-00891 and 2017-SGR-01479.© 2020 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes, creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works.

This paper presents a short review on the main high spectral efficient systems for multibeam satellite communications. In this regard, we study the use of Multi-User Detectors (MUD) and Successive Interference Cancellation (SIC) applied to aggressive frequency reuse, frequency packing and Non Orthogonal Multiple Access (NOMA). Furthermore, we have also considered the presence of co-channel inter- ference and spectrum limitations. The experimental validations have been conducted using DVB-S2 waveform. The results point out that the residual co-channel interference reduce the bene ts of using frequency packing schemes. Moreover, we investigate the e ect of asynchronous reception of data streams in our previously proposed interference management scheme based on cooperative NOMA in multibeam satellite systems. ; Grant numbers : This work has been funded from the Spanish Ministry of Science under project TERESA-TEC 2017-90093-C3-1-R; and from the Catalan Government (2017 SGR 891).

Next generation satellite payload technology is expected to provide digital processing capabilities. This will pave the way to regard satellites as flying base stations. However, the initial access procedure must be improved. In this work we focus on non-geostationary earth orbit (NGEO) satellite networks. In this scenario, the random access preamble signal and the detection must be robust to large carrier frequency offsets (CFOs). Towards this end, we investigate the adoption of the pruned discrete Fourier transform spread filter bank multicarrier waveform. The proposed design is suitable for the access scheme of forthcoming 5G-based NGEO satellite communications. The reason is twofold. First, it improves the spectral confinement with respect to the standard single-carrier frequency-division multiplexing (SC-FDM) waveform. Second, it achieves a high level of commonality with 5G new radio, by keeping unchanged the subcarrier spacing, the slot duration and the preamble sequence. Remarkably, the new design allows the straightforward application of non-coherent post detection integration (NCPDI) techniques, which divide the correlation in blocks. Numerical results show that the proposed solution reduces out-of-band emissions and the missed detection probability in presence of CFO, with respect to the conventional approach based on SC-FDM and preamble detection with full-length correlation. ; This work has received funding from the ministry of Science, Innovation and Universities under project TERESA-TEC2017-90093-C3-1-R (AEI/FEDER,UE) and under grant RTI2018-099841-B-I00 and from the Catalan Government (2017-SGR-1479). ; Peer Reviewed ; Postprint (author's final draft)

Machine-to-Machine (M2M) area networks connect a gateway with a huge number of energy-constrained end-devices. Therefore, energy efficiency is essential to prolong the lifetime of M2M networks. In this paper, we consider an M2M area network composed of hundreds or thousands of end-devices that periodically transmit data upon request from a gateway. We propose a Medium Access Control (MAC) protocol based on Frame Slotted-ALOHA (FSA) with Successive Interference Cancellation (SIC), also referred to as SIC-FSA, for data collection applications. By means of comprehensive computer-based simulations, we evaluate the delay and the energy consumed by the gateway and the enddevices using SIC-FSA. We have compared the delay and energy performance provided by SIC-FSA with that of conventional FSA and diversity-FSA (D-FSA). Results show that SIC-FSA can reduce the delay and energy consumption of the gateway in more than 50%, and the energy consumed by an end-device in more than 10%, with respect to FSA in dense M2M networks equipped with radio-transceivers in compliance with the IEEE 802.11 physical layer. ; Grant numbers : This work was supported in part by the Research Projects CO2GREEN (TEC2010-20823) and by the Catalan Government under grant 2009SGR1046.© 2014 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes, creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works.

The evaluation of the protocols in wireless systems is generally carried out by means of simulations. However, the large number of parameters of the radio link introduces a tradeoff between complexity and accuracy. This is the case of the systemlevel simulation of Ultra Narrow Band (UNB) signals over Low Earth Orbit (LEO) satellites. In order to overcome the complexity issue of this scenario, the proposed system-level simulator implements: i) physical layer abstraction methods, ii) sliding window strategies and iii) parallel architectures. Regarding the validness of the system-level simulations, it is necessary to have an accurate model of the physical layer. In particular, the system-level simulator has to know feasible pulse-shape filters, the minimum SINR at which the received data can be decoded, or the maximum collision bandwidth. Towards this regard, we have resorted to: i) convex optimization techniques for designing pulse-shape FIR filters with the frequency selectivity that the UNB signals require, ii) the Chi-square test for detecting the UNB frames with a predefined probability of false alarm, and iii) Discrete Fourier Transform (DFT) and Least Squares (LS) strategies for devising coarse and fine Carrier Frequency Offset (CFO) estimation algorithms. Furthermore, we explain how to compute the closed-form of the collision region between two UNB frames with time and frequency diversity in order to speed up system-level simulation. Results show that for SINRs larger than 8.5 dB it is possible to compensate the time and frequency drifts of IoT UNB signals over LEO, attain a BER lower than 1 10􀀀3, detect the UNB frames with a probability of false alarm of 0.01%, and design pulse-shape FIR filters with a moderate number of coefficients. ; Grant numbers : This work has received funding from the Spanish Ministry of Science, Innovation y Universities under project TERESATEC2017-90093-C3-1-R (AEI/FEDER,UE); and from the Catalan Government (2017 SGR 891 and 2017 SGR 1479).

Podeu consultar la versió en català a: http://hdl.handle.net/11703/113907 ; Podeu consultar la versió en anglès a: http://hdl.handle.net/11703/115653

Podeu consultar la versió en català a: http://hdl.handle.net/11703/113907 ; Podeu consultar la versió en castellà a: http://hdl.handle.net/11703/115635

Les mencions de responsabilitat s'han basat en els crèdits facilitats per l'àrea responsable ; Podeu consultar la versió en català a: http://hdl.handle.net/11703/106505 ; Podeu consultar la versió en castellà a: http://hdl.handle.net/11703/115663 ; Directrius per a definir el nou model de relació amb els proveïdors de tecnologia basat en el Codi de Pràctiques Tecnològiques

Les mencions de responsabilitat s'han basat en els crèdits facilitats per l'àrea responsable ; Podeu consultar la versió en català a: http://hdl.handle.net/11703/106505 ; Podeu consultar la versió en anglès a: http://hdl.handle.net/11703/115664 ; Directrius per a definir el nou model de relació amb els proveïdors de tecnologia basat en el Codi de Pràctiques Tecnològiques