(Please refer to the proposal for more details)
In this project, we aim at evaluating advanced cognitive radio techniques in case of satellite channel impairments and analyze the resulting performance loss. Afterwards, we will investigate different solutions to make them resilient to such impairments.
Machine-to-Machine (M2M) communications are one of the central use cases in fifth generation(5G) and beyond mobile network .  predicts the deployment of around 1 million devicesper km2. In this new environment and since available radio spectrum is today a scarce resource, one of the main faced challenges is the design of an efficient spectrum utilization anda better coordination between legacy (licensed) and future license-free services. Within thiscontext, satellite communication systems will play a key role in this deployment regardingtheir unique characteristics compared to terrestrial cellular networks, in terms of multicast andbroadcasting, mobility, global coverage (terrestrial cellular networks can cover only 20% of theEarth) with its ability to reach green spaces and hostile environments . With this in mind,the search for power and bandwidth efficiency as well as the actual trend to low complexitysatellite communication systems are of the upmost importance. The recent developments inspace-qualified Software Defined Radios (SDR)  as well as the maturity of advanced conceptssuch as flexible payloads  and nano-satellites make cognitive radio a promising and feasibleapproach for a smarter spectrum management, as this technology enables dynamic spectrumaccess and reconfigurability. Cognitive radio networks’ users exhibit different priorities (licensedradios usually coined as primary users (PU) and secondary radios (known as cognitive users(CU)). The difficulty is to limit the interference of CU to PU, while ensuring QoS for CUand managing efficiently the spectrum. Three paradigms emerge : (i) interweave: the CUtransmits opportunistically into the spaces not currently used by the PU; (ii) underlay: theCU adjusts its parameters in order to transmit simultaneously while respecting an interferencepower threshold and (iii) overlay: the CU has the prior knowledge of the PU message and, byusing judiciously chosen coding and signal processing techniques, is able to use simultaneouslythe PU channel (same frequency, time and polarization), without deteriorating this latter. Thefirst two schemes were well studied in [8, 9] and the last one has been investigated in thePhD thesis  (which will be defended at the beginning of 2020). In this latter, authorsfirstly derived a suitable system model, which takes into account the satellite parameters.This helps the analysis of the feasibility of such overlay cognitive radio techniques in the M2Msatellite context. Secondly, the authors proposed a practical implementation considering a trellisprecoding-based Dirty Paper Coding (TP-DPC) tranceiver. Thirdly, the authors developeddifferent schemes to control the transmitted CU power in different environments. Finally, asolution was proposed to deal with the so-called modulo loss. To progressively address theproblems (cognitive radio feasibility on one hand and satellite channel impairments on theother hand), all the proposed cognitive radio schemes have been optimized by considering asimplified transmission model (Gaussian-distributed noise and interference with quadrature-amplitude modulations (QAM)).
Problem and proposed solutions
In real scenarios, the satellite channel actually introduces various impairments (nonlinearitiesdue to the satellite transponder, phase noise, interference). In this project, we aim at evaluatingthe proposed techniques in  in case of satellite channel impairments and analyze the resulting performance loss. Afterwards, we will investigate different solutions to make them resilient tosuch impairments.
This postdoctoral research position is perfect for a highly-motivated researcher who wants toapply her/his solid skills in information coding and digital communications to satellite commu-nications. Applicants should:
Knowledge in satellite impairments or dirty paper coding would be a plus
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(c) GdR 720 ISIS - CNRS - 2011-2020.