Experimenting with commodity 802.11 hardware: overview and future directions

The huge adoption of 802.11 technologies has triggered a vast amount of experimentally-driven research works. These works range from performance analysis to protocol enhancements, including the proposal of novel applications and services. Due to the affordability of the technology, this experimental research is typically based on commercial off-the-shelf (COTS) devices, and, given the rate at which 802.11 releases new standards (which are adopted into new, affordable devices), the field is likely to continue to produce results. In this paper, we review and categorise the most prevalent works carried out with 802.11 COTS devices over the past 15 years, to present a timely snapshot of the areas that have attracted the most attention so far, through a taxonomy that distinguishes between performance studies, enhancements, services, and methodology. In this way, we provide a quick overview of the results achieved by the research community that enables prospective authors to identify potential areas of new research, some of which are discussed after the presentation of the survey.This work has been partly supported by the European Community through the CROWD project (FP7-ICT-318115) and by the Madrid Regional Government through the TIGRE5-CM program (S2013/ICE-2919).Publicad

Temporal Video Transcoding in Mobile Systems

La tesi analizza il problema della transcodifica temporale per la trasmissione del video in tempo reale su reti mobili. Viene proposta un’architettura di transcodifica temporale e un nuovo algoritmo di ricalcolo dei vettori di moto per il transcoder temporale H.264. Per fronteggiare il problema della riduzione costante della banda del canale wireless nelle reti infrastrutturate, vengono proposte diverse politiche di frame skipping basate sul dimensionamento del buffer del transcoder per garantire una comunicazione in tempo reale. Il moto di un frame e il numero di frames consecutivi scartati vengono inoltre considerati per migliorare la qualità del video transcodificato. E’ stato inoltre proposto e studiato un sistema di trasmissione video per reti veicolari con protocollo IEEE 802.11, basato su transcodifica temporale. Questo sistema permette di scartare quei frames il cui tempo di trasmissione supera un massimo ritardo ammisssibile al di sopra del quale tali frames non verrebbero comunque visualizzati. Il sistema proposto permette un notevole risparmio di banda e migliora la qualità del video evitando che molti frames consecutivi vengano scartati a causa della congestione

Dynamic and Dual Streaming Methods for H.264 Video and Parallel Performance Modeling

Traditional approaches to streaming H.264 video over a network typically rely on a single method of transport (i.e., reliable or unreliable) and/or use static values for parameters that can have a significant negative impact on the perceptual quality of the received video. This dissertation presents a dynamic method for wireless channel selection during video streaming, and explores the latency and QoE improvements yielded by the FDSP dual streaming method. The increased workload that results from these dynamic methods can lead to a counterproductive impairment of streaming performance, and therefore requires efficient use of the multiple cores typically present in both sender and receiver (or server and client). This dissertation therefore presents a performance cost model which can be used to guide the parallelization of specific types of client or server-side streaming components -- specifically, programs containing non-DOALL loops that have inter-iteration data dependences which constrain their parallelism