Optimum power allocation for parallel Gaussian channels with arbitrary input distributions

The mutual information of independent parallel Gaussian-noise channels is maximized, under an average power constraint, by independent Gaussian inputs whose power is allocated according to the waterfilling policy. In practice, discrete signalling constellations with limited peak-to-average ratios (m-PSK, m-QAM, etc) are used in lieu of the ideal Gaussian signals. This paper gives the power allocation policy that maximizes the mutual information over parallel channels with arbitrary input distributions. Such policy admits a graphical interpretation, referred to as mercury/waterfilling, which generalizes the waterfilling solution and allows retaining some of its intuition. The relationship between mutual information of Gaussian channels and nonlinear minimum mean-square error proves key to solving the power allocation problem.

High-SNR power offset in multiantenna communication

The analysis of the multiantenna capacity in the high-SNR regime has hitherto focused on the high-SNR slope (or maximum multiplexing gain), which quantifies the multiplicative increase as function of the number of antennas. This traditional characterization is unable to assess the impact of prominent channel features since, for a majority of channels, the slope equals the minimum of the number of transmit and receive antennas. Furthermore, a characterization based solely on the slope captures only the scaling but it has no notion of the power required for a certain capacity. This paper advocates a more refined characterization whereby, as function of SNRjdB, the high-SNR capacity is expanded as an affine function where the impact of channel features such as antenna correlation, unfaded components, etc, resides in the zero-order term or power offset. The power offset, for which we find insightful closed-form expressions, is shown to play a chief role for SNR levels of practical interest.

Capacity-achieving input covariance for single-user multi-antenna channels

We characterize the capacity-achieving input covariance for multi-antenna channels known instantaneously at the receiver and in distribution at the transmitter. Our characterization, valid for arbitrary numbers of antennas, encompasses both the eigenvectors and the eigenvalues. The eigenvectors are found for zero-mean channels with arbitrary fading profiles and a wide range of correlation and keyhole structures. For the eigenvalues, in turn, we present necessary and sufficient conditions as well as an iterative algorithm that exhibits remarkable properties: universal applicability, robustness and rapid convergence. In addition, we identify channel structures for which an isotropic input achieves capacity.

Capacity-approaching rate function for layered multiantenna architectures

The simultaneous use of multiple transmit and receive antennas can unleash very large capacity increases in rich multipath environments. Although such capacities can be approached by layered multi-antenna architectures with per-antenna rate control, the need for short-term feedback arises as a potential impediment, in particular as the number of antennas—and thus the number of rates to be controlled—increases. What we show, however, is that the need for short-term feedback in fact vanishes as the number of antennas and/or the diversity order increases. Specifically, the rate supported by each transmit antenna becomes deterministic and a sole function of the signal-to-noise, the ratio of transmit and receive antennas, and the decoding order, all of which are either fixed or slowly varying. More generally, we illustrate -through this specific derivation— the relevance of some established random CDMA results to the single-user multi-antenna problem.

Optimum power allocation for multiuser OFDM with arbitrary signal constellations

This paper formulates power allocation policies that maximize the region of mutual informationsachievable in multiuser downlink OFDM channels. Arbitrary partitioning ofthe available tones among users and arbitrary modulation formats, possibly different forevery user, are considered. Two distinct policies are derived, respectively for slow fadingchannels tracked instantaneously by the transmitter and for fast fading channels knownonly statistically thereby. With instantaneous channel tracking, the solution adopts theform of a multiuser mercury/waterfilling procedure that generalizes the single-user mercury/waterfilling introduced in [1, 2]. With only statistical channel information, in contrast,the mercury/waterfilling interpretation is lost. For both policies, a number of limitingregimes are explored and illustrative examples are provided.

Outage probability analysis for MRC in η-μ fading channels with co-channel interference

Exact closed-form expressions are obtained for the outage probability of maximal ratio combining in η-μ fadingchannels with antenna correlation and co-channel interference. The scenario considered in this work assumes the joint presence of background white Gaussian noise and independent Rayleigh-faded interferers with arbitrary powers. Outage probability results are obtained through an appropriate generalization of the moment-generating function of theη-μ fading distribution, for which new closed-form expressions are provided.

Mutual information of IID complex Gaussian signals on block Rayleigh-faded channels

We present a method to compute, quickly and efficiently, the mutual information achieved by an IID (independent identically distributed) complex Gaussian signal on a block Rayleigh-faded channel without side information at the receiver. The method accommodates both scalar and MIMO (multiple-input multiple-output) settings. Operationally, this mutual information represents the highest spectral efficiency that can be attained using Gaussiancodebooks. Examples are provided that illustrate the loss in spectral efficiency caused by fast fading and how that loss is amplified when multiple transmit antennas are used. These examples are further enriched by comparisons with the channel capacity under perfect channel-state information at the receiver, and with the spectral efficiency attained by pilot-based transmission.

Per-antenna rate and power control for MIMO layered architectures in the low- and high-power regimes

In a MIMO layered architecture, several codewordsare transmitted from a multiplicity of antennas. Although thespectral efficiency is maximized if the rates of these codewordsare separately controlled, the feedback rate within the linkadaptation loop is reduced if they are constrained to be identical.This poses a direct tradeoff between performance andfeedback overhead. This paper provides analytical expressionsthat quantify the difference in spectral efficiency between bothapproaches for arbitrary numbers of antennas. Specifically, thecharacterization takes place in the realm of the low- and highpowerregimes via expansions that are shown to have a widerange of validity.In addition, the possibility of adjusting the transmit powerof each codeword individually is considered as an alternative tothe separate control of their rates. Power allocation, however,turns out to be inferior to rate control within the context of thisproblem.

Mutual Information of IID complex Gaussian signals on block Rayleigh-faded channels

We present a method to compute, quickly and efficiently, the mutual information achieved by an IID (independent identically distributed) complex Gaussian signal on a block Rayleigh-faded channel without side information at the receiver. The method accommodates both scalar and MIMO (multiple-input multiple-output) settings. Operationally, this mutual information represents the highest spectral efficiency that can be attained using Gaussiancodebooks. Examples are provided that illustrate the loss in spectral efficiency caused by fast fading and how that loss is amplified when multiple transmit antennas are used. These examples are further enriched by comparisons with the channel capacity under perfect channel-state information at the receiver, and with the spectral efficiency attained by pilot-based transmission.

La influencia de la percepción de la imagen del locutor: estudio comparativo entre la voz del locutor aislada o asociada a una imagen

La voz es el esqueleto de la radio y su importancia en la comunicación radiofónica essustancial. Sin embargo son pocos los estudios que sobre ella se han realizado y menos aun los dedicados a comparar la impresión que una voz causa en el oyente cuando éste conoce la imagen del locutor y cuando la desconoce. Este estudio experimental muestra las reacciones manifestadas por un grupo de sujetos ante la escucha de una serie de voces y las compara con las expresadas por otro grupo de sujetos ante las mismas voces aunque en este caso en conocimiento de la imagen de los locutores. Los resultados apuntan a que los oyentes que desconocen la imagen del locutor tienden a recrear en sus mentes el aspecto del locutor mientras que los sujetos que conocen la imagen de éste se concentrar en imaginar el contenido de la noticia.

Projecte desplegament d'una xarxa d'operador de fibra òptica al 22@ i a diverses ciutats del continent

En la primera fase s’interconnectarien a través d’un anell de fibra òptica tres hotels d’una mateixa cadena en l’àrea del 22@ de Barcelona. S’ofereixen els serveis de: intranet, telefonia IP amb interconnexió a la PSTN, videoconferència i internet. Utilitzem VLANs per gestionar la qualitat de servei i la seguretat. El nostre model teòric inclou estimacions de tràfic, comparativa de fabricants, valoració econòmica i diagrama de Gantt d’implantació. A més, ampliem la gamma de serveis amb una xarxa Wimax al 22@ en previsió de futur ús. I augmentem la disponibilitat del servei amb un enllaç ràdio dedicat de backup des d’un dels nodes cap a la torre de Collserola, en la banda dels 18GHz, amb antenes parabòliques. Hem fet càlculs d’atenuació. En la segona i successives fases s’amplia la xarxa de FO a nivell nacional i internacional per a treballar com a operador d’empreses, amb un acurat disseny i selecció dels aparells òptics.

Bartók i els seus dos últims concerts

La idea inicial d’aquest projecte rau en el meu interès per aprofundir en dues obres: una, escrita per a viola, i l’altra, per a piano. La controvèrsia musicològica sobre l’autenticitat del Concert per a viola de Bartók, una obra cabdal dins del repertori d’aquest instrument, i la coincidència cronològica que aquest concert manté amb el Concert per a piano núm. 3 d’aquest mateix compositor han estat, finalment, el focus central de Bartók i els seus dos últims concerts. Mitjançant la informació extreta de llibres sobre el compositor, articles, tesis i partitures, les pàgines següents són el reflex del meu apropament als últims anys de la vida de Bartók, a la història que s’amaga darrere d’ambdues obres i als paral·lelismes que conté aquesta música.

Ses paraules juguen a quic: pervivència dels anglicismes introduïts al segle XVIII en la variant del català de Menorca

Treball de recerca realitzat per alumnes d’ensenyament secundari i guardonat amb un Premi CIRIT per fomentar l'esperit científic del Jovent l’any 2010. La variant dialectal del català de Menorca conserva algunes paraules d'origen anglès arran de la dominació britànica del segle XVIII. L'autor d'aquest treball ha dut a terme una recerca per a comprovar la pervivència de les paraules que l'últim estudi realitzat el 1983 havia constatat que eren d'ús habitual i comprovar si el pas del temps, el contacte amb altres llengües i la normalització lingüística, amb la introducció del català com a llengua vehicular en l'educació i la recepció de canals de ràdio i de televisió en català normatiu, havien tingut l'efecte d'anar substituint aquests mots. A través d'un exhaustiu treball de camp, amb un total de cent noranta-set entrevistes realitzades a peu de carrer de manera proporcional als habitants de les diferents poblacions de l'illa, d'est a oest, el mateix nombre per a cada gènere i dividides en grups per trams d'edat, l'autor va recollir les dades, a partir de les quals va fer l'anàlisi per passar a la seva posterior interpretació tenint en compte totes aquestes variables (gènere, territori i trams d'edat). Altres informacions complementàries recollides en el treball de camp van servir per a recolzar les conclusions. S’ha evidenciat que l'ús dels anglicismes es pot dividir en quatre grups: el dels que han desaparegut de la parla habitual; el dels que el seu ús decreix en funció de l'edat de les persones entrevistades; evidenciant la seva gradual desaparició; el dels que s'usen només en determinades poblacions i el dels que es mantenen ben vives arreu de l'illa, la majoria lligades a les festes o tradicions o al món de l'educació. Contràriament a la hipòtesi inicial, l'estudi ha constatat que la desaparició no es produeix en favor del terme corresponent en català estàndard, sinó per un castellanisme.

Contribución al diseño de GNSS-SDR, un receptor GNSS de código abierto

[ANGLÈS] This project introduces GNSS-SDR, an open source Global Navigation Satellite System software-defined receiver. The lack of reconfigurability of current commercial-of-the-shelf receivers and the advent of new radionavigation signals and systems make software receivers an appealing approach to design new architectures and signal processing algorithms. With the aim of exploring the full potential of this forthcoming scenario with a plurality of new signal structures and frequency bands available for positioning, this paper describes the software architecture design and provides details about its implementation, targeting a multiband, multisystem GNSS receiver. The result is a testbed for GNSS signal processing that allows any kind of customization, including interchangeability of signal sources, signal processing algorithms, interoperability with other systems, output formats, and the offering of interfaces to all the intermediate signals, parameters and variables. The source code release under the GNU General Public License (GPL) secures practical usability, inspection, and continuous improvement by the research community, allowing the discussion based on tangible code and the analysis of results obtained with real signals. The source code is complemented by a development ecosystem, consisting of a website (http://gnss-sdr.org), as well as a revision control system, instructions for users and developers, and communication tools. The project shows in detail the design of the initial blocks of the Signal Processing Plane of the receiver: signal conditioner, the acquisition block and the receiver channel, the project also extends the functionality of the acquisition and tracking modules of the GNSS-SDR receiver to track the new Galileo E1 signals available. Each section provides a theoretical analysis, implementation details of each block and subsequent testing to confirm the calculations with both synthetically generated signals and with real signals from satellites in space.

La premsa comarcal i el consum de noves pantalles

La investigació es centra en la visió dels mitjans de proximitat i el consum de d’aquests mitjans en el marc de la convergència digital a Catalunya. No és cap misteri l’aparició de nous hàbits de consum de continguts dels mitjans de comunicació nous i vells, on uns prefereixen, la premsa, la televisió i la ràdio, i d’altres amplien l’experiència i/o prefereixen la consulta de portals web, xarxes socials o continguts per internet a través de, dispositius mòbils, consoles de vídeojocs, etc. La recerca esta està dividida en dos grans blocs: per una banda, un estudi qualitatiu amb entrevistes en profunditat als responsables de mitjans comarcals sobre la seva visió com mitjà, i la seva trajectòria, i sobre els propis lectors, radiooients, i seguidors, ; i per l’altra banda, un quantitatiu mitjançant a partir d’una enquesta online a residents a Catalunya sobre el consum de mitjans. Les conclusions mostren una radiografia de l’actual ecosistema mediàtic a Catalunya.