How CSMA/CA With Deferral Affects Performance and Dynamics in Power-Line Communications

Power-line communications (PLC) are becoming a key component in home networking, because they provide easy and high-throughput connectivity. The dominant MAC protocol for high data-rate PLC, the IEEE 1901, employs a CSMA/CA mechanism similar to the backoff process of 802.11. Existing performance evaluation studies of this protocol assume that the backoff processes of the stations are independent (the so-called decoupling assumption). However, in contrast to 802.11, 1901 stations can change their state after sensing the medium busy, which is regulated by the so-called deferral counter. This mechanism introduces strong coupling between the stations and, as a result, makes existing analyses inaccurate. In this paper, we propose a performance model for 1901, which does not rely on the decoupling assumption. We prove that our model admits a unique solution for a wide range of configurations and confirm the accuracy of the model using simulations. Our results show that we outperform current models based on the decoupling assumption. In addition to evaluating the performance in steady state, we further study the transient dynamics of 1901, which is also affected by the deferral counter.Comment: To appear, IEEE/ACM Transactions on Networking 201

Enhancing scarce-resource language translation through pivot combinations

Chinese and Spanish are the most spoken languages in the world. However, there is not much research done in machine translation for this language pair. We experiment with the parallel Chinese-Spanish corpus (United Nations) to explore alternatives of SMT strategies which consist on using a pivot language. Particularly, two well-known alternatives are shown for pivoting: the cascade system and the pseudo-corpus. As Pivot language we use English, Arabic and French. Results show that English is the best pivot language between Chinese and Spanish. As a new strategy, we propose to perform a combination of the pivot strategies which is capable to highly outperform the direct translation strategy.Postprint (published version

Use of single-walled carbon nanotubes for near-infrared fluorescence within inner tissues in C. elegans

Anglès: Imaging and tracking long distance transport of proteins such as molecular motors with conventional fluorescence methodologies is nearly impossible mainly due to photobleaching. In this work we demonstrate that DNA-SWNTs are very convenient tagging particles for in vivo tracking of proteins due to their low toxicity and bright and stable fluorescence. Also, soft lithography is used to build a microfluidic trap for in vivo fluorescence imaging in C.elegans.Castellà: Hacer imágenes y seguir el transporte de proteínas como los motores moleculares a lo largo de distancias largas con técnica de fluorescencia convencionales es practicanete imposible debido al "photobleaching". En esta tesis demostramos que los ADN-SWNTs son unos marcadores de proteínas in vivo muy buenos gracias a su baja toxicidad y su fluorescencia estable e intensa. Además se utiliza litografía blanda para construir una trampa microfluidica para immobilizar un C.elegans y obtener imágenes de fluorescencia in vivo.Català: Fer imatges i seguir el transport de proteïnes com ara motors moleculars en distàncies llargues amb mètodes de fluorescència convencionals és quasi impossible a causa del "photobleaching". En aquesta tesi demostrem que els ADN-SWNTs són uns marcadors de proteïnes in vivo molt bons gracies a la seva baixa toxicitat i la seva fluorescència estable i intensa. A més, s'utilitza litografía tova per construir una trampa microfluidica per immobilitzar un C.elegans. i obtenir-ne imatges de fluorescència in vivo

A Client mobile application for Chinese-Spanish statistical machine translation

This show and tell paper describes a client mobile application for Chinese-Spanish machine translation. The system combines a standard server-based statistical machine translation (SMT) system, which requires online operation, with different input modalities including text, optical character recognition (OCR) and automatic speech recognition (ASR). It also includes an index-based search engine for supporting off-line translation.Postprint (published version

μ\muNap: Practical Micro-Sleeps for 802.11 WLANs

In this paper, we revisit the idea of putting interfaces to sleep during 'packet overhearing' (i.e., when there are ongoing transmissions addressed to other stations) from a practical standpoint. To this aim, we perform a robust experimental characterisation of the timing and consumption behaviour of a commercial 802.11 card. We design $\mu$Nap, a local standard-compliant energy-saving mechanism that leverages micro-sleep opportunities inherent to the CSMA operation of 802.11 WLANs. This mechanism is backwards compatible and incrementally deployable, and takes into account the timing limitations of existing hardware, as well as practical CSMA-related issues (e.g., capture effect). According to the performance assessment carried out through trace-based simulation, the use of our scheme would result in a 57% reduction in the time spent in overhearing, thus leading to an energy saving of 15.8% of the activity time.Comment: 15 pages, 12 figure