Nonasymptotic noisy lossy source coding

This paper shows new general nonasymptotic achievability and converse bounds and performs their dispersion analysis for the lossy compression problem in which the compressor observes the source through a noisy channel. While this problem is asymptotically equivalent to a noiseless lossy source coding problem with a modified distortion function, nonasymptotically there is a noticeable gap in how fast their minimum achievable coding rates approach the common rate-distortion function, as evidenced both by the refined asymptotic analysis (dispersion) and the numerical results. The size of the gap between the dispersions of the noisy problem and the asymptotically equivalent noiseless problem depends on the stochastic variability of the channel through which the compressor observes the source.Comment: IEEE Transactions on Information Theory, 201

Lossy joint source-channel coding in the finite blocklength regime

This paper finds new tight finite-blocklength bounds for the best achievable lossy joint source-channel code rate, and demonstrates that joint source-channel code design brings considerable performance advantage over a separate one in the non-asymptotic regime. A joint source-channel code maps a block of $k$ source symbols onto a length$-n$ channel codeword, and the fidelity of reproduction at the receiver end is measured by the probability $\epsilon$ that the distortion exceeds a given threshold $d$. For memoryless sources and channels, it is demonstrated that the parameters of the best joint source-channel code must satisfy $nC - kR(d) \approx \sqrt{nV + k \mathcal V(d)} Q(\epsilon)$, where $C$ and $V$ are the channel capacity and channel dispersion, respectively; $R(d)$ and $\mathcal V(d)$ are the source rate-distortion and rate-dispersion functions; and $Q$ is the standard Gaussian complementary cdf. Symbol-by-symbol (uncoded) transmission is known to achieve the Shannon limit when the source and channel satisfy a certain probabilistic matching condition. In this paper we show that even when this condition is not satisfied, symbol-by-symbol transmission is, in some cases, the best known strategy in the non-asymptotic regime

Fixed-length lossy compression in the finite blocklength regime

This paper studies the minimum achievable source coding rate as a function of blocklength $n$ and probability $\epsilon$ that the distortion exceeds a given level $d$. Tight general achievability and converse bounds are derived that hold at arbitrary fixed blocklength. For stationary memoryless sources with separable distortion, the minimum rate achievable is shown to be closely approximated by $R(d) + \sqrt{\frac{V(d)}{n}} Q^{-1}(\epsilon)$, where $R(d)$ is the rate-distortion function, $V(d)$ is the rate dispersion, a characteristic of the source which measures its stochastic variability, and $Q^{-1}(\epsilon)$ is the inverse of the standard Gaussian complementary cdf

Joint source-channel coding with feedback

This paper quantifies the fundamental limits of variable-length transmission of a general (possibly analog) source over a memoryless channel with noiseless feedback, under a distortion constraint. We consider excess distortion, average distortion and guaranteed distortion ($d$-semifaithful codes). In contrast to the asymptotic fundamental limit, a general conclusion is that allowing variable-length codes and feedback leads to a sizable improvement in the fundamental delay-distortion tradeoff. In addition, we investigate the minimum energy required to reproduce $k$ source samples with a given fidelity after transmission over a memoryless Gaussian channel, and we show that the required minimum energy is reduced with feedback and an average (rather than maximal) power constraint.Comment: To appear in IEEE Transactions on Information Theor

Metáfora, sinestesia y otras figuras retóricas en El perfume. Historia de un asesino, de P. Süskind

This article questions the author’s intention in the so frequent use of metaphors and other rhetorical figures in Perfume. History of a Murderer. This novel is a landmark in the German narrative of the XXth Century, due to the originality in the plot and to the great load of poetic images. Along with hyperbole, litotes, parallelism, personification, metonymy, comparison, polysindeton, and other figures, we will observe that it emphasizes metaphor, particularly literary synaesthesia. Within synaesthesia we will analyse the mixtures of senses and will classify the metaphors in their corresponding semantic fields. Finally, we analyse whether the use of such a number of tropes makes this work similar to some other literary tendencies within the universal narrative of the XXth century, and whether Süskind’s poetic and sensorial narrative might be included in any literary trend of the XXth centuryEl siguiente artículo cuestiona la intención de su autor en el empleo tan frecuente de metáforas y otras figuras retóricas en El perfume. Historia de un asesino. Hemos escogido esta novela porque marca un hito en la narrativa alemana del S. XX debido a la originalidad en el argumento y a la gran carga de imágenes poéticas. Junto con hipérbole, lítote, paralelismo, personificación, metonimia, comparación, polisíndeton, y otras figuras, observaremos que destaca la metáfora, en concreto la sinestesia literaria. Dentro de la sinestesia analizaremos las mezclas de sentidos en ella y clasificaremos las metáforas en sus correspondientes campos semánticos. Finalmente nos cuestionamos si el empleo de tan elevado número de tropos aproxima esta obra a alguna otra corriente literaria dentro de la narrativa universal del S. XX. Queda abierta una línea de debate que cuestiona la similitud de la narrativa tan poética y sensorial de Süskind y la posible inclusión de este autor en alguna corriente literaria del S. XX

Utilidad de las nuevas tecnologías en lengua alemana para universitarios. Experiencias didácticas desde un enfoque constructivista

En el siguiente artículo exponemos experiencias educativas realizadas en la universidad de Castellón durante tres cursos consecutivos y que integran las nuevas tecnologías e Internet en la enseñanza de alemán con óptimos resultados. En primer lugar nos centramos en la videoconferencia y sus aplicaciones prácticas en clase de lengua alemana. Describimos una experiencia realizada por video conferencia con otra universidad en Alemania. Especificamos el tipo de actividades que mejor se adaptaron a la videoconferencia, así como los objetivos comunicativos y los beneficios que se derivaron del empleo de la misma. En segundo lugar ofrecemos una definición y explicación detallada de lo que es un proyecto email, sin duda más factible en la mayoría de escuelas. Posteriormente analizamos los resultados de esta experiencia y la influencia que tuvo en la motivación de nuestros alumnos

Fixed-length lossy compression in the finite blocklength regime: discrete memoryless sources

This paper studies the minimum achievable source coding rate as a function of blocklength n and tolerable distortion level d. Tight general achievability and converse bounds are derived that hold at arbitrary fixed blocklength. For stationary memoryless sources with separable distortion, the minimum rate achievable is shown to be q closely approximated by R(d) + √v(d)/nQ^(-1)(ϵ), where R(d) is the rate-distortion function, V (d) is the rate dispersion, a characteristic of the source which measures its stochastic variability, Q-1 (·) is the inverse of the standard Gaussian complementary cdf, and ϵ is the probability that the distortion exceeds d. The new bounds and the second-order approximation of the minimum achievable rate are evaluated for the discrete memoryless source with symbol error rate distortion. In this case, the second-order approximation reduces to R(d) + 1/2 log n/n if the source is non-redundant

Channels With Cost Constraints: Strong Converse and Dispersion

This paper shows the strong converse and the dispersion of memoryless channels with cost constraints and performs a refined analysis of the third-order term in the asymptotic expansion of the maximum achievable channel coding rate, showing that it is equal to (1/2)((log n)/n) in most cases of interest. The analysis is based on a nonasymptotic converse bound expressed in terms of the distribution of a random variable termed the mathsf b -tilted information density, which plays a role similar to that of the mathsf d -tilted information in lossy source coding. We also analyze the fundamental limits of lossy joint-source-channel coding over channels with cost constraints