1,720,957 research outputs found
Multiuser MIMO downlink systems with limited feedback and remote sensing of vital signs
Get PDFThis PhD thesis collects the main contribution of my research activity, performed during my PhD program. As the title suggests, it is divided into two main parts.
The first part collects the research I performed since the beginning of my PhD on Multiuser multiple input multiple output (MIMO) downlink systems with limited feedback; the topic is part of the wide research work on the fourth generation cellular systems.
When I begun my research, on January 2007, most of the theoretical analysis had already been illustrated; therefore, my work focused on optimizing system parameters considering the limited resources available in a realistic scenario. The main contributions are on the design of the low rate feedback channel, and sub-optimal, low complexity scheduling algorithms, both in single carrier and in a orthogonal frequency division multiplexing (OFDM) scenario.
The second, and most recent part of the thesis deals with remote sensing of vital signs, i.e. respiration and heart rate; I have been addressing this topic since October 2008, in cooperation with Philips Research, Eindhoven (NL), where I have been visiting student.
We investigated the ultra wide band technology for remote sensing of vital signs. We propose a generic model for the received signal and described how vital sign modulates the main parameters of the received signal. Furthermore, we focused on detection techniques of respiration and heart beating periods;
we derived the ML period estimator of a zero mean signal with unknown shape, and we proposed a novel low complexity approximated ML estimator.
The proposed methods have application in many areas where only the periodicity is
required and the complexity is an important issue.
In particular, we applied the proposed algorithms to the remote heart rate estimation problem; both simulation and experimental results indicate that the proposed method outperforms the state of the art methods in detecting the period of a signal with low signal to noise ratio like the heart beating, even with a short observation of the periodic signal.
%Communication and radar ha complementary a
Though the two parts of research I performed during my PhD program seem to have little in common, they can be investigated with the same analytical tools, particularly for signal processing and detection techniques.Questa tesi di dottorato raccoglie i contributi principali dell'attività di ricerca svolta durante i tre anni del mio percorso di dottorato. Come suggerisce il titolo, l'attivita' di ricerca condotta in questo triennio è divisa in due parti principali. La prima riguarda l'argomento di ricerca che ho seguito sin dall'inizio sui sistemi di downlink Multiuser MIMO con feedback limitato; è parte di un ampio filone di ricerca finalizzato alla progettazione della quarta generazione di sistemi cellulari, e piu' in generale di futuri sistemi di comunicazioni wireless con terminali mobili.
In particolare, i miei studi si sono concentrati sui sistemi cellulari in cui le stazioni base sono provviste di antenne multiple; la presenza di piu' antenne alla stazioni base fornisce dei gradi di liberta' nelle comunicazioni di downlink, ovvero nelle comunicazioni dalla stazioni base ai terminali mobili, che possono essere utilizzati per servire piu' di un utente simultaneamente e ottenere un rate piu' elevato rispetto al caso singola antenna. A tal fine e' pero' necessario fornire alla stazioni base la conoscenza dei canali di downlink per ciascuno degli utenti che intende servire; tanto piu' fine e' la stima del canale in possesso della stazioni base, tanto maggiore e' il rate raggiungibile in questo schema di downlink. La progettazione di strategie di feedback, con cui i terminali trasmettono su un canale dedicato informazioni sul canale di downlink alla stazioni base e' quindi un aspetto di grande interesse, essendo il canale di feedback a rate limitato (dell'ordine di qualche bit/simbolo). In particolare, mi sono occupata della scelta del quantizzatore e delle strategie di feedback che tenessero conto della correlazione temporale del canale. All'inizio del triennio (gennaio 2007) la maggior parte delle analisi teorica era stata sviluppata; di conseguenza, il mio lavoro è incentrato sull'ottimizzazione dei parametri del sistema, tenendo conto delle limitate risorse disponibili in uno scenario realistico.
I contributi principali riguardano la progettazione del canale di feedback a rate limitato e algoritmi di scheduling subottimi a bassa complessità, sia per sistemi single carrier che in uno scenario OFDM.
In particolare, i contributi riguardanti la progettazione del canale di feedback a rate limitato traggono vantaggio dalla correlazione temporale del canale, utilizzando sistemi di quantizzazione con memoria.
E' stato inoltre proposto un algoritmo di scheduling a bassa complessita', e si sono studiate le prestazioni in confronto con i principali algoritmi presenti in letteratura.
Tale confronto evidenzia che a parita' di condizioni, l'algoritmo da noi proposto e' caratterizzato da prestazioni analoghe alle altre soluzioni e molto vicine all'ottimo, sia in termini di throughput che di outage throughput, ma con una minor complessita'.
La seconda e più recente parte della tesi affronta l'argomento della stima di segnali vitali, ovvero la respirazione e il battito cardiaco, attraverso un sistema remoto, dove non c'e' contatto tra il sensore ed il target a distanza. Questo argomento e' stato affrontato, in collaborazione con Philips Research, Eindhoven (NL), dove sono stata come Visiting Student da ottobre 2008 a maggio 2009. Ho studiato la tecnologia ultra wide band per il rilevamento remoto dei segni vitali, con il vincolo di rispettare i limiti di potenza imposti dalla legislazione vigente. Lo studio e' stato condotto sia analiticamente, che tramite simulazioni, ed infine attraverso l'allestimento di una demo e la raccolta di risultati sperimentali.
In particolare, ho proposto un modello generico per il segnale ricevuto e descritto analiticamente la modulazione che i segnali vitali operano sui principali parametri del segnale ricevuto.
Sulla base di questo modello, ho studiato le tecniche di rilevazione del respiro e del cuore periodi di battere; in particolare, ho proposto un metodo di stima del periodo a bassa complessita', che migliora le prestazioni di altre soluzioni proposte in letteratura, sia in termini di errore quadratico medio che di complessita' richiesta.
Infine, è stato derivato lo stimatore maximum likelihood (ML), ed è stato verificato che il metodo proposto risulta da un'approssimazione del metodo ML
ML period estimation with application to vital sign monitoring
No full textThe real time estimation of the period of signals that are periodic over short time intervals requires fast algorithms. In this letter, the maximum likelihood (ML) period estimator is derived for a periodic signal with additive white Gaussian noise. A low complexity approximation is then proposed, and compared with the state of the art of the estimation techniques in a practical scenario for the remote estimation of human heart rate using an ultra wide band radar
Heart rate estimation using ultra wide band pulse radar
No full textUltra Wide Band radar is a promising technique for remote vital signs monitoring. For home monitoring and consumer devices, FCC rules pose severe limits to the available band and the maximum transmitted power. Furthermore, the time varying nature of vital signs, and the demand of low complexity devices require simple detection algorithms. In this paper vital signs are monitored with a FCC compliant system; in this scenario, low signal to noise ratio and short signal observations are the main issues for period detection. Therefore, a simple detection algorithm is proposed and compared with the widely used correlation based detection algorithm. Both theoretical analysis and experimental re sults show the efficiency of the proposed algorithm in the considered scenario
A Comparison of Scheduling Strategies for MIMO Broadcast Channel with Limited Feedback on OFDM Systems
Get PDFWe consider a multiuser downlink transmission from a base station with multiple antennas (MIMO) to mobile terminals (users) with a single antenna, using orthogonal frequency division multiplexing (OFDM). Channel conditions are reported by a feedback from users with limited rate, and the base station schedules transmissions and beamforms signals to users. We show that an important set of schedulers using a general utility function can be reduced to a scheduler maximizing the weighted sum rate of the system. For this case we then focus on scheduling methods with many users and OFDM subcarriers. Various scheduling strategies are compared in terms of achieved throughput and computational complexity and a good tradeoff is identified in greedy and semiorthogonal user selection algorithms. In the greedy selection algorithm, users are selected one by one as long as the throughput increases, while in the semiorthogonal approach users are selected based on the channel correlation. An extension of these approaches from a flat-fading channel to OFDM is considered and simplifications that may be useful for a large number of subcarriers are presented. Results are reported for a typical cellular transmission of the long-term evolution (LTE) of 3GPP
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
- …
