654 research outputs found
DVB-H Antenna in a small Handheld Device
Get PDFDigital Video Broadcasting for Handheld devices (DVB-H) is a technical specification for bringing broadcast services to handheld receivers. It will be possible to watch TV mobile devices such as mobile phones. However, since the typical size of a mobile phone is small compared to the wavelength of the transmitted DVB-H signals, designing the internal antenna is very challenging. In this Master Thesis we focused our attention on internal tuneable antennas that we simulated using FDTD technique. We investigated the previous work done on DVB-H antennas as a starting point. It appeared that the use of matching circuits was necessary to cover the whole band of interest to have a good trade-off between the antenna size and its performances. However, simple matching techniques such as L networks were not efficient enough. This is why we focused on broadband matching technique. We used a simple wire as antenna and improved its performances using Chebyshev matching filters. The whole DVB-H band has been covered using less than half the number of previously used matching circuits. This improved consequently the performances while minimizing the total losses
Impact of channel models in MIMO OFDM for LTE
No full textIn this report, a study of OFDM receiver algorithms for SISO, SIMO, and MIMO with SMUX and STBC is performed. The algorithms are compared using BER simulations in an uncorrelated Rayleigh fading channel. The system is extended to include Turbo coding and rate matching complying with the LTE standard, reaching a throughput of 11.2~bits/sec/Hz in an i.i.d. 2x2 Rayleigh fading channel. To maximize the advantage from the Turbo codes, a soft decision demodulator for M-PSK and M-QAM modulation constellations is developed.Finally, the attention is brought to channel models with spatial correlation, created from statistics and geometry. A geometrically based channel model is developed and evaluated with respect to the Demmel Condition Number, and a comparison between this and the WINNER~II channel model is performed.Based on the findings in this study, it is concluded that additional antennas add a significant gain in throughput, specifically by obtaining additional diversity from STBC in the low SNR regime and SMUX in the high SNR regime
Novel small-size directional antenna for UWB WBAN/WPAN applications
Get PDFThis paper presents a novel small-size directional antenna design for ultrawide-band wireless body area networks/wireless personal area networks applications. The design is based on a typical slot antenna structure with an added reflector in order to achieve directionality. The effects of different antenna parameters and human body proximity on the radiation characteristics are analyzed. Antenna measurements with an optic RF setup were performed in order to characterize the small-size antenna far field radiation pattern. The different structural antenna parameters were optimized via extensive numerical simulations. Results show that for frequencies above 3.5 GHz, where the power front-to-back ratio of the directional antenna is greater than 10 dB, its impedance is nearly the same as in the free space. It is not the case neither for the omnidirectional slot antenna nor the monopole antenna next to the body. Between 3 and 6 GHz performance of the novel directional antenna, in terms of radiation efficiency and SAR values, is significantly improved compared to omnidirectional antenna designs.This paper presents a novel small-size directional antenna design for ultrawide-band wireless body area networks/wireless personal area networks applications. The design is based on a typical slot antenna structure with an added reflector in order to achieve directionality. The effects of different antenna parameters and human body proximity on the radiation characteristics are analyzed. Antenna measurements with an optic RF setup were performed in order to characterize the small-size antenna far field radiation pattern. The different structural antenna parameters were optimized via extensive numerical simulations. Results show that for frequencies above 3.5 GHz, where the power front-to-back ratio of the directional antenna is greater than 10 dB, its impedance is nearly the same as in the free space. It is not the case neither for the omnidirectional slot antenna nor the monopole antenna next to the body. Between 3 and 6 GHz performance of the novel directional antenna, in terms of radiation efficiency and SAR values, is significantly improved compared to omnidirectional antenna designs
Firm Spin-offs in Denmark 1981-2000 - Patterns of Entry and Exit
Get PDFThe motivation of this paper is to add new, large sample evidence on the extent to which the likelihood of business failure or success is related to relationships between parent firms and their 'off-spring'. For this purpose we make use of an exhaustive matched employer-employee data set covering the entire Danish private sector in years 1981 to 2000 to study firm entry and exit. Special focus is on spin-offs, a particular group of small entries, which are founded by groups of persons originating from the same former workplace. We estimate a multinomial logit model in order to examine which characteristics of the founders and the parent firms increase the probability of spinning off. Next, we carry out a duration analysis of the subsequent transitions of the spin-offs, and compare their exit risks with those of other entries, which have less strong parent-progeny relationships in terms of worker flows. With respect to entry, poor performance of the parent firm is found to be a key determinant of the decision to spin off. The spin-offs are shown to have a lower death risk than the comparison group, also after controlling for a host of firm and employee characteristics. The exit risks of spin-offs and the comparison group are observed to converge over time. However, when we cater for unobserved heterogeneity the convergence turns out to be predominantly an outcome of selection rather than the result of other start-ups catching up via some learning process. For the entire sample of entries, we find a positive association between size of the entry and survival probability, and a countercyclical sensitivity of exit risk.Entry; Exit; Spin-offs; Duration analysis
Agent-Based Modeling of Culture's Consequences for Trade
No full textIn this thesis, culture is interpreted as a property of a group of people who share the meaning they attach to symbols, have a common way of expressing their opinions and feelings, and share value systems to judge what is good or bad. The unwritten rules of a culture govern the interpretation of observations and emotions and how to react appropriately. The rules are embedded in an individuals’ mind, form childhood on, by interactions with group members. People often are not aware of differences between their own unwritten rules and those of people having a different cultural background. This may result in unwarranted distrust or unwarranted trust, with serious consequences for the future of relationships. Cultural differences are known to have their effects on trade. Signals that indicate benevolence and trustworthiness of a trade partner in one’s own culture may be interpreted differently by people having a different cultural background. Hofstede (2001) has identified five dimensions of cultural differences: ? Given ingroup relation with relatives and community members may have a different impact on professional relationships in different cultures. ? The impact of hierarchical relationships on the freedom of action of trade partners may be different across cultures. ? Some cultures are oriented toward cooperation and care-taking; others are oriented toward performance and competition. ? Xenophobia is a wide-spread phenomenon in some cultures, while people in other cultures may be more open to the unknown. ? In some cultures people are anxious to keep up their status and display their societal success, while in other cultures thrift and perseverance are seen as virtues. Cultural differences may have their effects in trade on the acceptability of potential partners, on progress and success of negotiations, and on the extent to which partners live up to the negotiated contracts. In a research project Meijer (2009) developed a gaming simulation to study the role of trust in supply networks of food products. The game is called the TRUST & TRACING game. In this game, the producers are informed about product quality. The other players either have to trust the suppliers on their quality statements, or they can have the products traced by an independent authority, but the latter will cost them a fee. In addition to the financial considerations, they must take into account that showing distrust may bring damage to their relationships. Experiments with human subjects in different cultures have shown that the considerations lead to different actions in different countries. It was also found that the inclination to grab an opportunity to defect was different across countries. The subject of this thesis is a computer simulation of the TRUST & TRACING GAME. The purposes of the computer simulation are: ? Validation of theories about, implemented in models of, the players’ behaviors ? testing of hypotheses about relations of rules of the game and parameters of individual players with aggregated game statistics, ? the design of useful game configurations to be played with human players. In the computer simulation the players’ rolls are realized by software agents. The questions which are answered in this thesis concern the modeling of culture’s consequences for the decisions taken by the agents. Such an agent is a computer program which simulates the behavior of human players. In a multi-agent simulation a group of software agents is acting and interacting simultaneously. Autonomy is an important property of software agents. The agents decide what to do; there is no central computer program that imposes decisions on them. Important functions of agents in the present simulation are to approach new potential trade partners, to negotiate about a transaction and to exchange proposals, and, when the negotiation has ended successfully, to exchange products, and to decide and request a trace to be performed. The agents’ decision mechanisms are implemented according to models and data available from scientific literature. To model the influence of culture on the decision making, an expert systems approach is taken, using the Synthetic Cultures according to Hofstede en Pedersen (1999). To develop an expert system, knowledge engineers represent knowledge about some domain of application as a set of rules that can be interpreted by a computer system. Since culture is considered as a set of rules, such an approach is a natural way to model it. The development of expert systems always is an interdisciplinary project. In this case the work of Geert Hofstede has been used and an expert on this work and on Synthetic Cultures has been involved in the formulation of the rules. Synthetic Cultures are imaginary cultures in which the effects of a single dimension of culture are emphasized, isolated from the effects of the other dimensions. The purpose is to make the differences related to that dimension teachable. In reality the differences may be less pronounced and may be mixed with differences related with the other dimensions. In this thesis an approach has been elaborated to compute the simultaneous effect of several dimensions. The approach is based on the principle of weak disjunction, which implies that, if several dimensions have a similar effect, only the strongest effects counts. For instance, if dimension A would have an effect of 75% and dimension B would have an effect of 25%, then their simultaneous effect would be 75%. Expert systems must at least have face validity. An expert in the domain of application mustaccept the decisions that the system produces and the reasoning that leads to these decisions, as being believable. For this purpose computations for specific cases can be made, of which the results are judged by the expert. Further, the results of sensitivity analysis can be judged by an expert. Sensitivity analysis of a model is performed by studying how model outputs vary in relation with systematic variation of input parameter. In addition to face validity, the model must be tested empirically. To that end outputs from gaming simulations with human participants can be compared with outputs from multi-agent simulations. For example, Meijer et al. (2006) found different outcomes from the TRUST & TRACING game between games played in the United States and in the Netherlands. Compared with the Dutch, American players are found to be more eager to buy top quality products, have a stronger inclination to opportunism, anticipate to a greater extent on their partners to defect, and have a stronger preference for quality certification. These differences where reproduced by the multi-agent simulation. The main question of this research is, whether an expert systems approach is feasible to develop a valid model of cultural differentiation in multi-agent simulations, to be applied in research with gaming simulations. The conclusions are: 1. Effects of dimensions of culture can be modeled as an expert system based on Synthetic Cultures. Modeling the simultaneous effects of several dimensions as an expert system proved not feasible: the complexity exceeded the intellectual powers of both expert and modeler. 2. The simultaneous effect of several dimensions can be modeled by weak disjunction of effects. The results have face validity and have empirically been verified for a limited number of cases. 3. Sensitivity analysis of this model is a complex undertaking if both cultural parameters and other parameters are simultaneously varied, because of the strong interactions between these types of parameters. When only the culture parameters are varied (with a fixed setting of the other parameters), or only the other parameters are varied (in a fixed cultural setting), straightforward sensitivity analysis is feasible. Furthermore, it was found that the sensitivity of aggregate model outputs may greatly differ from sensitivity of individual level outputs: parameters that do not affect the aggregate system performance, may affect results of individual agents. 4. This thesis proves that multi-agent simulation is a potent instrument to be used in research with gaming simulations, in particular for the purpose of validation of behavioral models. A problematic issue is, that similarity of the outputs of gaming simulations and multi-agent simulations is no sound proof that the agent correctly implements the human decision making mechanism. This issue is known as under-determination. A validation method is proposed, which builds on the model’s composed structure. Under-determination can be avoided by separate validation of the components in micro-games. The results of this research contribute to the methodology of cultural adaptation of intelligent software agents. This is relevant for the development of research instruments (like the TRUST & TRACING game), educational and training applications to make people aware of cultural differences, and affective human-computer interfaces in a globalizing world.MediamaticsElectrical Engineering, Mathematics and Computer Scienc
An Infinite Analogue of Rings with Stable Rank One
No full textAbstractReplacing invertibility with quasi-invertibility in Bass' first stable range condition we discover a new class of rings, the QB-rings. These constitute a considerable enlargement of the class of rings with stable rank one (B-rings) and include examples like EndF(V), the ring of endomorphisms of a vector space V over some field F, and B(F), the ring of all row- and column-finite matrices over F. We show that the category of QB-rings is stable under the formation of corners, ideals, and quotients, as well as matrices and direct limits. We also give necessary and sufficient conditions for an extension of QB-rings to be a QB-ring, and show that extensions of B-rings often lead to QB-rings. Specializing to the category of exchange rings we characterize the subset of exchange QB-rings as those in which every von Neumann regular element extends to a maximal regular element, i.e., a quasi-invertible element. Finally we show that the C*-algebras that are QB-rings are exactly the extremally rich C*-algebras studied by L. G. Brown and the second author
Tuning Range Optimization of a Planar Inverted F Antenna for LTE Low Frequency Bands
No full textThis paper presents a Planar Inverted F Antenna (PIFA) tuned with a fixed capacitor to the low frequency bands supported by the Long Term Evolution (LTE) technology. The tuning range is investigated and optimized with respect to the bandwidth and the efficiency of the resulting antenna. Simulations and mock-ups are presented
Excising States of <i>C</i>*-Algebras
No full textA net {aα} of positive, norm one elements of a C*-algebra A excises a state f of A ifThis notion has been used explicitly by the second author [4, 5, 6] for pure states, but the present paper will explore it more fully. The name is motivated by the following example. Let K be the unit disk in the complex plane, A = C(K) and f(a) = a(0). Define an(reiθ) = ϕn(r), whereNote that the sets {t ∊ K:an(t) ∊ 0} form rings about 0 with radii tending to 0. In this sense the sequence {an} “cuts out” the state f and, in the limit, isolates it from all other states.</jats:p
Small Open Economy Firms in International Trade: Evidence from Danish Transactions-Level Data
Get PDFIn this paper, we use a rich dataset disaggregating imports and exports decisions by product and origin/destination of all Danish companies for the period 1993-2003 to provide key elements in characterizing Danish firms in international trade. Most evidence to date emanates from the U.S. or developing economies like Columbia or Mexico. Benchmarking on these studies, we find some similarities but also differences which we think are representative of European-type, small open economies. We find that Danish exporters make up a fairly small fraction of the total of firms, but that this fraction is higher than in e.g., the U.S. Firms engaged in exporting have the same positive performance characteristics – size, capital and skilled labour intensity, labour as well as total factor productivity, and wages – found in also in previous studies. But most exporter premia are significantly larger in Denmark than in the U.S. There are few traces of the European Union’s Single Market Program and the adoption the Euro in 1998. We observe no impact of these changes on the number of exporters, but some signs of impacts on the number of products and export destination countries. Finally, we find that trade is positively related to productivity of firms. The association between productivity and the firm’s imports of intermediate goods is particularly strong.Exporters; exporter premium; firm heterogeneity
On the Currents Magnitude of a Tunable Planar-Inverted-F Antenna for Low-Band Frequencies
Get PDFTunable antennas are a promising way to overcome bandwidth limitations for the new communication standards. Nevertheless they become very lossy at low frequencies. This paper presents an investigation on the currents running through the source, the short and the capacitor of a tunable Planar Inverted F Antenna (PIFA) for hand-held devices. Simulations suggest that the losses due to the currents running through the external tuning component depend on its location and value. Therefore it should be placed the furthest away from the location of the source and the short in a PIFA design and have small capacitances
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