114 research outputs found

    Energy and rate allocation for massive multiple access with interference cancelation

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    This article addresses the problem of energy and code allocation to many users accessing, under spreading-based nonorthogonal multiple access, a wireless node set up with a successive interference cancellation architecture aided by redundancy-check error control. As an application, we consider the asynchronous access of a delay-tolerant satellite system, where users employ finite-length channel codes and are subject to a known power unbalance induced by the known distribution of the channel’s attenuation. The article develops, as a mathematically tractable approximation to massively populated systems, a unified framework to compute the best energy and code allocation rules that maximize the spectral efficiency of a network that handles asymptotically many users. Concretely, the presented approach circumvents the exponential complexity in the number of users when modeling the propagation of packet decoding failures through the receiver’s decoding scheme. It also enables a deterministic analysis of the more complex features affecting the receiver, making the related performance optimization problem amenable to systematic tools from differential and variational calculus. The derived expressions evidence the most favorable three-way unbalance between energy, rate, and reliability for receiver performance. Low-level system simulations are carried out for validation.This work was supported in part by the Spanish Ministry of Science and Innovation through project RODIN (PID2019-105717RB-C22/AEI/10.13039/501100011033) and in part by Grant 2017 SGR 578.Peer ReviewedPostprint (published version

    Correlation study between the access mark and the performance in project-based and standard courses

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    The access mark to engineering studies is often used as an a priori success estimator. In our institution, we have observed that the correlation of the access mark with the grades obtained in project-based courses (R=0.52) is slightly lower than the one obtained with the average of the other non-project-based courses (R=0.58), and is especially low in capstone projects (R=0.31). Project-based and Challenge-based courses are one of the most acknowledged ways of promoting the learning of transversal skills, specifically innovation and entrepreneurship skills. In our institution, ICT engineering bachelor students perform a project-courses path, with three subjects of growing complexity in the 2nd, 3d and 4th year. While the first two are partially guided and with challenges proposed by the faculty members, the 3d one is a 12 ECTS capstone project with challenges proposed by industry or external institutions. In this study, we have analyzed the performance of the students along 10 academic years (2011-2012 to 2020-2021). Not only the correlation with the access mark in these courses is lower but the prediction interval is also different. While it is almost impossible that a student with a low access mark gets an outstanding average mark in the bachelor and vice-versa, there are students with a low access mark which have an outstanding performance in the capstone project and students with a very high access mark and with high results in analytical courses but with a poor performance in capstone projects. Therefore, a different kind of skills are promoted in these courses

    SENYALS I SISTEMES LINEALS (Examen 1r quadrimestre)

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    Examen final amb solucióResolve

    SENYALS I SISTEMES LINEALS (Examen 2n quadrimestre)

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    Segon parcial sense soluci

    Variance processing for stable boundary-layer height estimation using backscatter lidar data: A discussion

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    In this paper we present a method for estimating the height of the nocturnal stable boundary layer by using lidar measurements and a single radiosonde for unambiguous initial guess. The method relies on the correlation between aerosol stratifications in the stable boundary layer and minimum variance levels in the attenuated backscatter profile. The method is based on calculating either temporal or spatial variance vertical profiles of the attenuated backscatter and threshold-limited decision. A radiosonde temperature-based estimation is used to provide an initial guess if several minimum variance regions are detected. Two study cases using ceilometer data are shown. Comparison with temperature-based estimations from a collocated microwave radiometer have been used for validation. The method can be useful for estimating the stable boundary layer height in sites with a ceilometer but without any available temperature profiler.This work was supported via Spanish Government‚ÄďEuropean Regional Development Funds project PGC2018-094132-B-I00 and EU H2020 ACTRIS-IMP (GA 871115). CommSensLab is a Mar√≠a-de-Maeztu Unit of Excellence funded by the Agencia Estatal de Investigaci√≥n, Spain. The work of M.P. Araujo da Silva was supported by the Spanish Ministry of Science, Innovation and Universities under Grant PRE2018-086054. Data were provided by J√ľlich Observatory for Cloud Evolution (JOYCE-CF), a core facility funded by Deutsche Forschungsgemeinschaft via grant DFG LO 901/7-1.Peer ReviewedPostprint (author's final draft

    Examen final de reavaluació, curs 2018-2019: enunciat i solucions genèriques

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    Examen final, del qual existeix la resoluci√≥ detallada del professor Sisco Vallverd√ļ Bay√©sResolve

    SENYALS I SISTEMES LINEALS (Examen 2n quadrimestre)

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    Examen final amb solució i problema proposatResolve

    Examen final del quadrimestre de tardor, curs 2017-2018: enunciat

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    Examen final, del qual existeix la resoluci√≥ detallada del professor Sisco Vallverd√ļ Bay√©

    Channel-aware energy allocation for throughput maximization in massive low-rate multiple access

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    © 2019 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.A multiple access (MA) optimization technique for massive low-rate direct-sequence spread spectrum communications is analyzed in this work. A dense network of users transmitting at the same rate to a common central node under channelaware energy allocation is evaluated. At reception, successive interference cancellation (SIC) aided by channel decoding is adopted. Our contribution focuses on wireless scenarios involving a vast number of users for which the provided user-asymptotic model holds. Variational calculus (VC) is employed to derive the energy allocation function that, via user-power imbalance, maximizes the network spectral efficiency (SE) when perfect channel state information at transmission (CSIT) is available and both average and maximum per-user energy constraints are set. Monte Carlo simulations at chip-level of a SIC receiver using a real decoder assess the proposed optimization method.Peer ReviewedPostprint (published version

    Decentralized random energy allocation for massive non-orthogonal code-division multiple access

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    © 2019 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 work studies the spectral efficiency achievable when a very large number of terminals are connected simultaneously to a central node (uplink) through independent and identically-distributed flat-fading channels. Assuming that terminals only have statistical channel state information (CSI), the optimum random transmitted-energy allocation is formulated considering a non-orthogonal direct-sequence code-division multiple access (DS-CDMA) where all users transmit using the same modulation and error correcting code and the receiver implements successive interference cancellation (SIC). Focusing on low-power terminals, optimization is carried out by imposing constraints on both the average and peak peruser transmitted energy. Simulations have revealed that a limited number of random energy levels, whose number is determined by the channel power gain variance, is sufficient to achieve approximately the maximum spectral efficiency that would be obtained under direct optimization of the received energy profile.Peer ReviewedPostprint (author's final draft
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