Conduit artery structure and function in lowlanders and native highlanders: relationships with oxidative stress and role of sympathoexcitation

Research detailing the normal vascular adaptions to high altitude is minimal and often confounded by pathology (e.g. chronic mountain sickness) and methodological issues. We examined vascular function and structure in: (1) healthy lowlanders during acute hypoxia and prolonged (∼2 weeks) exposure to high altitude, and (2) high-altitude natives at 5050 m (highlanders). In 12 healthy lowlanders (aged 32 ± 7 years) and 12 highlanders (Sherpa; 33 ± 14 years) we assessed brachial endothelium-dependent flow-mediated dilatation (FMD), endothelium-independent dilatation (via glyceryl trinitrate; GTN), common carotid intima–media thickness (CIMT) and diameter (ultrasound), and arterial stiffness via pulse wave velocity (PWV; applanation tonometry). Cephalic venous biomarkers of free radical-mediated lipid peroxidation (lipid hydroperoxides, LOOH), nitrite (NO₂^–) and lipid soluble antioxidants were also obtained at rest. In lowlanders, measurements were performed at sea level (334 m) and between days 3–4 (acute high altitude) and 12–14 (chronic high altitude) following arrival to 5050 m. Highlanders were assessed once at 5050 m. Compared with sea level, acute high altitude reduced lowlanders’ FMD (7.9 ± 0.4 vs. 6.8 ± 0.4%; P = 0.004) and GTN-induced dilatation (16.6 ± 0.9 vs. 14.5 ± 0.8%; P = 0.006), and raised central PWV (6.0 ± 0.2vs. 6.6 ± 0.3 m s⁻¹; P = 0.001). These changes persisted at days 12–14, and after allometrically scaling FMD to adjust for altered baseline diameter. Compared to lowlanders at sea level and high altitude, highlanders had a lower carotid wall:lumen ratio (∼19%, P ≤ 0.04), attributable to a narrower CIMT and wider lumen. Although both LOOH and NO₂^– increased with high altitude in lowlanders, only LOOH correlated with the reduction in GTN-induced dilatation evident during acute (n = 11, r = −0.53) and chronic (n = 7, r = −0.69; P ≤ 0.01) exposure to 5050 m. In a follow-up, placebo-controlled experiment (n = 11 healthy lowlanders) conducted in a normobaric hypoxic chamber (inspired O₂ fraction () = 0.11; 6 h), a sustained reduction in FMD was evident within 1 h of hypoxic exposure when compared to normoxic baseline (5.7 ± 1.6 vs. 8.0 ±1.3%; P < 0.01); this decline in FMD was largely reversed following α₁-adrenoreceptor blockade. In conclusion, high-altitude exposure in lowlanders caused persistent impairment in vascular function, which was mediated partially via oxidative stress and sympathoexcitation. Although a lifetime of high-altitude exposure neither intensifies nor attenuates the impairments seen with short-term exposure, chronic high-altitude exposure appears to be associated with arterial remodelling.

Movement and Perceptual Strategies to Intercept Virtual Sound Sources

To intercept a moving object, one needs to be in the right place at the right time. In order to do this, it is necessary to pick up and use perceptual information that specifies the time to arrival of an object at an interception point. In the present study, we examined the ability to intercept a laterally moving virtual sound object by controlling the displacement of a sliding handle and tested whether and how the interaural time difference (ITD) could be the main source of perceptual information for successfully intercepting the virtual object. The results revealed that in order to accomplish the task, one might need to vary the duration of the movement, control the hand velocity and time to reach the peak velocity (speed coupling), while the adjustment of movement initiation did not facilitate performance. Furthermore, the overall performance was more successful when subjects employed a time-to-contact (tau) coupling strategy. This result shows that prospective information is available in sound for guiding goal-directed actions.

Comment on ''Sedimentary DNA from a submerged site reveals wheat in the British Isles 8000 years ago''

Smith et al. (Reports, 27 February 2015, p. 998) identify wheat DNA from an 8000-calendar-years-before-the-present archaeological site in southern England and conclude that wheat was traded to Britain 2000 years before the arrival of agriculture. The DNA samples are not dated, either directly or from circumstantial evidence, so there is no chronological evidence to support the claim

A study exploring disordered eating patterns in first-year university students: student and service needs

This qualitative study explored disordered eating in a small group of first-year undergraduate students and addresses a gap in the literature by exploring their lived experience.

Aims: To better understand student’s needs in those experiencing or at risk of developing disordered eating during their first year at university and to illustrate what support mechanisms and services are required to better support students experiencing or at risk during their first year at university.

Conclusion: The University could further develop its outreach to new students with a more consistently supportive programme providing better facilities and training for stress appraisal and coping and more support via student buddying. The University could also extend its programme on positive mental health in an attempt to better inform on disordered eating and to reduce a sense of stigma within the student population. Personal tutors and student health care facilities need to be consistently trained in the understanding and person centred approach to students experiencing disordered eating, particularly the sub-clinical group. In addition the University could consider some small changes and adaptations to the refectory eating areas to better facilitate students who may be at risk from disordered eating. Finally the University could perhaps better use the potentially liminal period within the first few months of student's arrival at university (a new beginning) to help embed a program to develop a stronger sense of coherence and well-being.

Radiocarbon chronology for the Early Gravettian of northern Europe : new AMS determinations for Maisieres-Canal, Belgium

The authors explore the arrival of the earliest Gravettian in north-west Europe, using new high precision radiocarbon dates for bone excavated at Maisieres-Canal in Belgium to define a short-lit^ed occupation around 33 000 years ago. The tanged points in that assemblage have parallels in British sites, including Goat's Hole (Paviland). This is the site of the famous ochred burial of a young adult male, confiisingly known as the 'Red Lady', notv dated to around 34 000 BP. The new results demonstrate that this British 'rich burial' and the Gravettian with tanged points may bebng to two different occupation horizons separated by a cold spell.

A tool for the evaluation of slaughter horse welfare during unloading

This study aimed to develop a scientific and practical tool to be used to assess horse welfare after commercial transport over long journeys. A set of physical, behavioural and environmental measures was selected, covering welfare aspects of both transport and unloading procedures. The protocol was field-tested on 51 intra-EU commercial transports arriving at different sites in Italy. Univariate analysis was implemented to look for associations between the input variables (environmental hazards potentially affecting the animal well-being during long transports) and the outcome variables (direct evaluation of the animal condition). No severe welfare impairments were recorded (ie dead on arrival, severe injuries, non-ambulatory animals), while milder ones were more frequent at unloading (eg slipping; 36.7%, reluctance to move; 9.6%). Correlations emerged between ramp slope and falling; type of ramp floor and slipping; fast gait and the presence of gaps between the ramp and the floor. The horses' behaviour was also related to the type of handling procedure used. The measures were repeatable and practical to apply and score during real-time unloading. This work provides a sound basis for a new and practical welfare assessment tool for horses travelling over long journeys. Careful and constant application of this protocol would provide stakeholders with the opportunity to track and monitor changes in the industry over time, as well as to identify high risk areas in transport routines.

The Pine Wood Nematode: a personal view

The first report of the disease (“pine wilt disease”) associated with the pinewood nematode, goes back to 1905, when Yano reported an unusual decline of pines from Nagasaki. For a long time thereafter, the cause of he disease was sought, but without success. Because of the large number of insect species that were usually seen around and on infected trees, it had always been assumed that the causal agent would prove to be one of these. However, in 1971, Kiyohara and Tokushike found a nematode of the genus Bursaphelenchus in infected trees. The nematode found was multiplied on fungal culture, inoculated into healthy trees and then re-isolated from the resulting wilted trees. The subsequent published reports were impressive: this Bursaphelenchus species could kill fully-grown trees within a few months in the warmer areas of Japan, and could destroy complete forests of susceptible pine species within a few years. Pinus densiflora, P. thunbergii und P. luchuensis were particularly affected. In 1972, Mamiya and Kiyohara described the new species of nematode extracted from the wood of diseased pines; it was a named Bursaphelenchus lignicolus. Since 1975, the species has spread to the north of Japan, with the exception of the most northerly prefectures. In 1977, the loss of wood in the west of the country reached 80%. Probably as a result of unusually high summer temperatures and reduced rainfall in the years 1978 and 1979, the losses were more than 2 million m3 per year. From the beginning, B. lignicolus was always considered by Japanese scientists to be an exotic pest. But where did it come from? That this nematode could also cause damage in the USA became clear in 1979 when B. lignicolus was isolated in great numbers from wood of a 39 year-old pine tree (Pinus nigra) in Missouri which had suddenly died after the colour of its needles changed to a reddish-brown colour (Dropkin und Foudin, 2 1979). In 1981, B. lignicolus was synonymised by Nickle et al. with B. xylophilus which had been found for the first time in the USA as far back as 1929, and reported by Steiner and Buhrer in 1934. It had originally been named Aphelenchoides xylophilus, the wood-inhabiting Aphelenchoides but was recognised by Nickle, in 1970,to belong in the genus Bursaphelenchus. Its common name in the USA was the "pine wood nematode" (PWN. After its detection in Missouri, it became known that B. xylophilus was widespread throughout the USA and Canada. It occurred there on native species of conifers where, as a rule, it did not show the symptoms of pine wilt disease unless susceptible species were stressed eg., by high temperature. This fact was an illuminating piece of evidence that North America could be the homeland of PWN. Dwinell (1993) later reported the presence of B. xylophilus in Mexico. The main vector of the PWN in Japan was shown to be the long-horned beetle Monochamus alternatus, belonging to the family Cerambycidae. This beetle lays its eggs in dead or dying trees where the developing larvae then feed in the cambium layer. It was already known in Japan in the 19th century but in the 1930s, it was said to be present in most areas of Japan, but was generally uncommon. However, with the spread of the pine wilt disease, and the resulting increase of weakened trees that could act as breeding sites for beetles, the populations of Monochamus spp. increased significantly In North America, other Monochamus species transmit PWN, and the main vector is M. carolinensis. In Japan, there are also other, less efficient vectors in the genus Monochamus. Possibly, all Monochamus species that breed in conifers can transmit the PWN. The occasional transmission by less efficient species of Monochamus or by some of the many other beetle genera in the bark or wood is of little significance. In Europe, M. galloprovincialis and M. sutor transmits the closely related species B. mucronatus. Some speculate that these two insect species are “standing by” and waiting for the arrival of B. xylophilus. In 1982, the nematode was detected and China. It was first found in dead pines near the Zhongshan Monument of Nanjing (CHENG et. al. 1983); 265 trees were then killed by pine wilt disease. Despite great efforts at eradication in China, the nematode spread further and pine wilt disease has been 3 reported from parts of the provinces of Jiangsu, Anhui, Guangdong, Shandong, Zhejiang and Hubei (YANG, 2003). In 1986, the spread of the PWN to Taiwan was discovered and in 1989, the nematode was reported to be present in the Republic of Korea where it had first been detected in Pinus thunbergii and P. densiflora. It was though to have been introduced with packing material from Japan. PWN was advancing. In 1984, B. xylophilus was found in wood chips imported into Finland from the USA and Canada, and this was the impetus to establish phytosanitary measures to prevent any possible spread into Europe. Finland prohibited the import of coniferous wood chips from these sources, and the other Nordic countries soon followed suit. EPPO (the European and Mediterranean Plant Protection Organization) made a recommendation to its member countries in 1986 to refuse wood imports from infested countries. With its Directive of 1989 (77/93 EEC), the European Community (later called the European Union or EU) recognised the potential danger of B. xylophilus for European forests and imposed restrictions on imports into the Europe. PWN was placed on the quarantine list of the EU and also of other European countries. Later, in 1991, a dispensation was allowed by the Commission of the EU(92/13 EEC) for coniferous wood from North America provided that certain specified requirements were fulfilled that would prevent introduction.

Gerações de ecrã em meio rural : estudo dos novos media no quotidiano rural português de três gerações

Desde finais da década de 50, com o aparecimento e progressiva disseminação da televisão pelas casas portuguesas (atualmente, numa parte significativa delas, existe em mais do que um compartimento); passando pelo computador, na década de 70; e, finalmente, a forma como, na década de 90, se iniciou o processo de distribuição do telemóvel, há toda uma história associada sobre a qual é importante refletir. No meio rural português, qual foi o caminho traçado pelos seus residentes até à “domesticação” (Berker, Hartmann, Punie, & Ward, 2005; Silverstone, Hirsch, & Morley, 1992) de cada um dos media – televisão, computador e telemóvel? Da utilização quase exclusiva em espaços públicos até à sua integração no espaço doméstico e nas dinâmicas familiares e sociais, houve um percurso percorrido quer pelos media, que vão sofrendo alterações constantes, quer pelos indivíduos que se vão adaptando a essas alterações, mas também exigindo que os primeiros se vão moldando às suas necessidades e exigências, fazendo, por isso, que nunca percam o epíteto de “novo”. A existência dos meios digitais tem ainda outras particularidades associadas: a sua presença diária e transversal em todos os contextos nos quais os indivíduos estão habitualmente inseridos – familiar, laboral/escolar e de lazer -, a ocorrência em todas as gerações familiares e, consequentemente, de um modo generalizado, em todas as idades. Os avós, os pais (e, ao mesmo tempo, filhos) e os filhos (e, ao mesmo tempo, netos) fazem uma utilização mais ou menos frequente, mas que não é inexistente, originando, por isso, a designação de gerações de ecrã. Interessa, pois, fazer o estudo dos usos e apropriações dos novos media pelas diferentes gerações, para uma análise intergeracional, mas, mais ainda, compreender as implicações que esses usos têm no meio rural, por ser fortemente considerado como uma zona em desvantagem quanto à proliferação dos media e das tecnologias de informação e comunicação, quando comparada com a urbana. Apresenta-se uma análise e reflexão sobre o modo como os novos media penetraram no quotidiano de três gerações familiares (avós, pais e filhos) e na forma como estas, residentes no meio rural português, transformaram a apropriação dos media num ato contínuo. Esta análise e reflexão fundamentam-se no levantamento bibliográfico sobre a problemática e os dados empíricos obtidos através da aplicação de uma metodologia triangular: focus groups, diários e inquéritos por questionário.

Ultrasonic location system

Esta tese apresenta um sistema de localização baseado exclusivamente em ultrassons, não necessitando de recorrer a qualquer outra tecnologia. Este sistema de localização foi concebido para poder operar em ambientes onde qualquer outra tecnologia não pode ser utilizada ou o seu uso está condicionado, como são exemplo aplicações subaquáticas ou ambientes hospitalares. O sistema de localização proposto faz uso de uma rede de faróis fixos permitindo que estações móveis se localizem. Devido à necessidade de transmissão de dados e medição de distâncias foi desenvolvido um pulso de ultrassons robusto a ecos que permite realizar ambas as tarefas com sucesso. O sistema de localização permite que as estações móveis se localizem escutando apenas a informação em pulsos de ultrassons enviados pelos faróis usando para tal um algoritmo baseado em diferenças de tempo de chegada. Desta forma a privacidade dos utilizadores é garantida e o sistema torna-se completamente independente do número de utilizadores. Por forma a facilitar a implementação da rede de faróis apenas será necessário determinar manualmente a posição de alguns dos faróis, designados por faróis âncora. Estes irão permitir que os restantes faróis, completamente autónomos, se possam localizar através de um algoritmo iterativo de localização baseado na minimização de uma função de custo. Para que este sistema possa funcionar como previsto será necessário que os faróis possam sincronizar os seus relógios e medir a distância entre eles. Para tal, esta tese propõe um protocolo de sincronização de relógio que permite também obter as medidas de distância entre os faróis trocando somente três mensagens de ultrassons. Adicionalmente, o sistema de localização permite que faróis danificados possam ser substituídos sem comprometer a operabilidade da rede reduzindo a complexidade na manutenção. Para além do mencionado, foi igualmente implementado um simulador de ultrassons para ambientes fechados, o qual provou ser bastante preciso e uma ferramenta de elevado valor para simular o comportamento do sistema de localização sobre condições controladas.

Cooperative positioning for heterogeneous wireless systems

Future emerging market trends head towards positioning based services placing a new perspective on the way we obtain and exploit positioning information. On one hand, innovations in information technology and wireless communication systems enabled the development of numerous location based applications such as vehicle navigation and tracking, sensor networks applications, home automation, asset management, security and context aware location services. On the other hand, wireless networks themselves may bene t from localization information to improve the performances of di erent network layers. Location based routing, synchronization, interference cancellation are prime examples of applications where location information can be useful. Typical positioning solutions rely on measurements and exploitation of distance dependent signal metrics, such as the received signal strength, time of arrival or angle of arrival. They are cheaper and easier to implement than the dedicated positioning systems based on ngerprinting, but at the cost of accuracy. Therefore intelligent localization algorithms and signal processing techniques have to be applied to mitigate the lack of accuracy in distance estimates. Cooperation between nodes is used in cases where conventional positioning techniques do not perform well due to lack of existing infrastructure, or obstructed indoor environment. The objective is to concentrate on hybrid architecture where some nodes have points of attachment to an infrastructure, and simultaneously are interconnected via short-range ad hoc links. The availability of more capable handsets enables more innovative scenarios that take advantage of multiple radio access networks as well as peer-to-peer links for positioning. Link selection is used to optimize the tradeo between the power consumption of participating nodes and the quality of target localization. The Geometric Dilution of Precision and the Cramer-Rao Lower Bound can be used as criteria for choosing the appropriate set of anchor nodes and corresponding measurements before attempting location estimation itself. This work analyzes the existing solutions for node selection in order to improve localization performance, and proposes a novel method based on utility functions. The proposed method is then extended to mobile and heterogeneous environments. Simulations have been carried out, as well as evaluation with real measurement data. In addition, some speci c cases have been considered, such as localization in ill-conditioned scenarios and the use of negative information. The proposed approaches have shown to enhance estimation accuracy, whilst signi cantly reducing complexity, power consumption and signalling overhead.

Sectorial antennas for WSN localization system

This work investigates low cost localization systems (LS) based on received signal strength (RSS) and integrated with different types of antennas with main emphasis on sectorial antennas. The last few years have witnessed an outstanding growth in wireless sensor networks (WSN). Among its various possible applications, the localization field became a major area of research. The localization techniques based on RSS are characterized by simplicity and low cost of integration. The integration of LS based on RSS and sectorial antennas (SA) was proven to provide an effective solution for reducing the number of required nodes of the networks and allows the combination of several techniques, such as RSS and angle of arrival (AoA). This PhD thesis focuses on studying techniques, antennas and protocols that best meet the needs of each LS with main focus on low cost systems based on RSS and AoA. Firstly there are studied localization techniques and system that best suit the requirements of the user and the antennas that are most appropriate according to the nature of the signal. In this step it is intended to provide a fundamental understanding of the undertaken work. Then the developed antennas are presented according to the following categories: sectorial and microstrip antennas. Two sectorial antennas are presented: a narrowband antenna operating at 2.4 to 2.5 GHz and a broadband antenna operating at 800MHz-2.4GHz. The low cost printed antennas were designed to operate at 5 GHz, which may be used for vehicular communication. After presenting the various antennas, several prototypes of indoor/outdoor LS are implemented and analyzed. Localization protocols are also proposed, one based on simplicity and low power, and the other on interoperability with different types of antennas and system requirements.

A integração de media sociais nas organizações de gestão de destinos: proposta de um modelo orientador para a utilização de media sociais nas atividades de comunicação com os turistas

Sendo o turismo um dos setores económicos onde a informação desempenha um papel fundamental, é, também, um dos mais afetados com a chegada da nova realidade que são os media sociais. Atualmente, devido à utilização generalizada de aplicações da Web 2.0 e, sobretudo, devido ao crescimento exponencial da utilização de aplicações de media sociais, verifica-se que esta utilização está a provocar alterações significativas na promoção dos destinos turísticos, com uma estratégia clara destes passarem a utilizar os conteúdos gerados pelos utilizadores na Internet. Perante este novo paradigma, as Organizações de Gestão de Destinos, como organizações dinâmicas cujo objetivo é a promoção dos destinos turísticos, têm que se adaptar de forma a enquadrar esta nova realidade. O presente trabalho pretende, pois, analisar a forma como as Organizações de Gestão de Destinos portuguesas utilizam a Internet, e em particular as aplicações da Web 2.0/media sociais nas suas estratégias de comunicação. Assim, pretende-se fazer uma análise da situação atual em que se encontram as Organizações de Gestão de Destinos Portuguesas, na utilização deste tipo de aplicações para, a partir daí, se desenvolver uma proposta de modelo orientador para a utilização de media sociais nas atividades de comunicação com os turistas, que permita explorar ao máximo este enorme potencial. Como resultado desta investigação, espera-se contribuir para uma melhor compreensão de como as Organizações de Gestão de Destinos Portuguesas devem usar as aplicações de media sociais nas suas estratégias de comunicação por aplicação da proposta de modelo desenvolvida.

Ensino superior como princípio hegemónico de cidadania na sociedade civil: um diálogo com António Gramsci no sul da Amazónia brasileira

A tese tem como foco quatro eixos centrais: o ensino superior, a sociedade civil, a cidadania e a hegemonia. Na primeira parte da tese, estes eixos teórico-conceptuais são explanados numa perspectiva da promoção de uma compreensão mais ampla da sociedade civil e do estado, nomeadamente o contratualismo, o liberalismo, o materialismo e o neoliberalismo. Um protagonismo fundamental é atribuído às concepções de Antonio Gramsci de sociedade civil, cidadania e estado aplicadas no ensino superior no Sul da Amazónia brasileira. A segunda parte da tese concentra-se num estudo de caso com três premissas de análise: a fragmentação do ensino superior brasileiro; a reconfiguração da cidadania e hegemonia; e o ensino superior no contexto do Amazonas. O ensino superior no Brasil teve início com as escolas jesuíticas, que, depois de encerradas pelo Marquês de Pombal não tiveram sucessoras em solo brasileiro, ao nível do que poderia ter sido o embrião de um sistema de ensino superior. A chegada da Corte Imperial Portuguesa, em 1808, permite reinstalar novos cursos. A primeira unidade de ensino superior no Amazonas surge apenas no princípio do século XX. Um século depois, tem início o processo de expansão com a implantação de unidades no interior do estado. O ensino superior no Brasil, nas últimas décadas, assumiu um caráter híbrido e de massificação. A massificação, no entanto, ainda é uma realidade a ser alcançada. Apesar dos avanços realizados na última década, ainda subsiste ainda uma forte exclusão de estudantes. O enfoque sobre o ensino superior e a cidadania, no contexto do Amazonas, surge na articulação de um conjunto de informação empírica, extraída de entrevistas realizadas com atores chave locais, com as categorias de pensamento de Antonio Gramsci, que sustentam teoricamente o estudo. Esta articulação tem no ensino superior a possibilidade de desenvolver a cidadania como o princípio organizador e fim último deste nível de ensino. Neste sentido, a hegemonia ganha um estatuto de orientação e direção que permite aos sujeitos envolvidos no ensino superior maior possibilidade de autonomia, liberdade, justiça social, empregabilidade e desenvolvimento social. O modelo de universidade para a cidadania apresenta-se como uma possibilidade de mudanças no horizonte social, económico e também político, no interior da própria universidade. O ensino superior, perspectivado como um instrumento essencial para a cidadania, tem como objetivo primordial a qualificação de professores para a educação de base, Reflexivamente, esta qualificação não deixará potencialmente de produzir retornos positivos na própria expansão e abrangência numérica e educativa do próprio ensino superior. Desta forma, a cidadania no ensino superior é perspectivada neste estudo como um deslocamento de lógicas de compreensão individual e de individualização elitista dos benefícios para lógicas assentes em construções mais coletivas, portadoras de benefícios sociais. A interiorização do ensino superior no Amazonas é assumida no estudo como uma possibilidade de formação académica para o desenvolvimento de práticas pedagógicas e científicas críticas e mais conscientes, constituindo um horizonte determinante para a ativação de processos de integração regional e nacional. Em suma, os pontos de confluência entre o ensino superior, a sociedade civil, a cidadania e as propostas de Gramsci, estão relacionados com a formação, a conscientização política, e o bem-estar económico e social.

In search of reliable centimeter-level indoor positioning: a smartphone-based approach

This thesis describes the design and implementation of a reliable centimeter-level indoor positioning system fully compatible with a conventional smartphone. The proposed system takes advantage of the smartphone audio I/O and processing capabilities to perform acoustic ranging in the audio band using non-invasive audio signals and it has been developed having in mind applications that require high accuracy, such as augmented reality, virtual reality, gaming and audio guides. The system works in a distributed operation mode, i.e. each smartphone is able to obtain its own position using only acoustic signals. To support the positioning system, a Wireless Sensor Network (WSN) of synchronized acoustic beacons is used. To keep the infrastructure in sync we have developed an Automatic Time Synchronization and Syntonization (ATSS) protocol with a standard deviation of the sync offset error below 1.25 μs. Using an improved Time Difference of Arrival (TDoA) estimation approach (which takes advantage of the beacon signals’ periodicity) and by performing Non-Line-of-Sight (NLoS) mitigation, we were able to obtain very stable and accurate position estimates with an absolute mean error of less than 10 cm in 95% of the cases and a mean standard deviation of 2.2 cm for a position refresh period of 350 ms.

Channel modelling for MIMO systems

Systems equipped with multiple antennas at the transmitter and at the receiver, known as MIMO (Multiple Input Multiple Output) systems, offer higher capacities, allowing an efficient exploitation of the available spectrum and/or the employment of more demanding applications. It is well known that the radio channel is characterized by multipath propagation, a phenomenon deemed problematic and whose mitigation has been achieved through techniques such as diversity, beamforming or adaptive antennas. By exploring conveniently the spatial domain MIMO systems turn the characteristics of the multipath channel into an advantage and allow creating multiple parallel and independent virtual channels. However, the achievable benefits are constrained by the propagation channel’s characteristics, which may not always be ideal. This work focuses on the characterization of the MIMO radio channel. It begins with the presentation of the fundamental results from information theory that triggered the interest on these systems, including the discussion of some of their potential benefits and a review of the existing channel models for MIMO systems. The characterization of the MIMO channel developed in this work is based on experimental measurements of the double-directional channel. The measurement system is based on a vector network analyzer and a two-dimensional positioning platform, both controlled by a computer, allowing the measurement of the channel’s frequency response at the locations of a synthetic array. Data is then processed using the SAGE (Space-Alternating Expectation-Maximization) algorithm to obtain the parameters (delay, direction of arrival and complex amplitude) of the channel’s most relevant multipath components. Afterwards, using a clustering algorithm these data are grouped into clusters. Finally, statistical information is extracted allowing the characterization of the channel’s multipath components. The information about the multipath characteristics of the channel, induced by existing scatterers in the propagation scenario, enables the characterization of MIMO channel and thus to evaluate its performance. The method was finally validated using MIMO measurements.