Average Rate of Downlink Heterogeneous Cellular Networks over Generalized Fading Channels - A Stochastic Geometry Approach

In this paper, we introduce an analytical framework to compute the average rate of downlink heterogeneous cellular networks. The framework leverages recent application of stochastic geometry to other-cell interference modeling and analysis. The heterogeneous cellular network is modeled as the superposition of many tiers of Base Stations (BSs) having different transmit power, density, path-loss exponent, fading parameters and distribution, and unequal biasing for flexible tier association. A long-term averaged maximum biased-received-power tier association is considered. The positions of the BSs in each tier are modeled as points of an independent Poisson Point Process (PPP). Under these assumptions, we introduce a new analytical methodology to evaluate the average rate, which avoids the computation of the Coverage Probability (Pcov) and needs only the Moment Generating Function (MGF) of the aggregate interference at the probe mobile terminal. The distinguishable characteristic of our analytical methodology consists in providing a tractable and numerically efficient framework that is applicable to general fading distributions, including composite fading channels with small- and mid-scale fluctuations. In addition, our method can efficiently handle correlated Log-Normal shadowing with little increase of the computational complexity. The proposed MGF-based approach needs the computation of either a single or a two-fold numerical integral, thus reducing the complexity of Pcov-based frameworks, which require, for general fading distributions, the computation of a four-fold integral.Comment: Accepted for publication in IEEE Transactions on Communications, to appea

TRIZ as Seen through the DIMAI Creative Thinking Model

Abstract The aim of this paper is to show that TRIZ is not an isolated theory, but a set of tools that can be interpreted in the light of general theoretical models for creativity. In fact, the numerous tools and strategies that TRIZ formulates can be seen as specific instances of the DIMAI model for the creative thinking process, which takes into account environmental, personality, and cognitive factors and postulates five principal states: Drive, Information, Movement, Assessment and Implementation. Letting "strategy" be defined as a sequence of activation of states, components or sub-processes that includes implementation as a final step, we show how TRIZ offers a systematic organization of strategies for the disciplined and aware use of the complex interactions between the cognitive, individual and emotional elements hypothesized into the DIMAI model. The interpretation of TRIZ through the DIMAI model is not only interesting from a theoretical point of view, but it adds an awareness layer which can help both the scientist and the practitioner in dealing systematically and homogeneously with the multiple variables and elements involved in the creative and innovative act, thus enhancing the overall effectiveness

Nonlinear bivariate comovements of asset prices: Theory and tests

Comovements among asset prices have received a lot of attention for several reasons. For example, comovements are important in cross-hedging and cross-speculation; they determine capital allocation both domestically and in international mean–variance portfolios and also, they are useful in investigating the extent of integration among financial markets. In this paper we propose a new methodology for the non–linear modelling of bivariate comovements. Our approach extends the ones presented in the recent literature. In fact, our methodology outlined in three steps, allows the evaluation and the statistical testing of non-linearly driven comovements between two given random variables. Moreover, when such a bivariate dependence relationship is detected, our approach solves for a polynomial approximation. We illustrate our three–steps methodology to the time series of energy related asset prices. Finally, we exploit this dependence relationship and its polynomial approximation to obtain analytical approximations of the Greeks for the European call and put options in terms of an asset whose price comoves with the price of the underlying asset

Fractal Markets Hypothesis and the Global Financial Crisis: Scaling, Investment Horizons and Liquidity

We investigate whether fractal markets hypothesis and its focus on liquidity and invest- ment horizons give reasonable predictions about dynamics of the financial markets during the turbulences such as the Global Financial Crisis of late 2000s. Compared to the mainstream efficient markets hypothesis, fractal markets hypothesis considers financial markets as com- plex systems consisting of many heterogenous agents, which are distinguishable mainly with respect to their investment horizon. In the paper, several novel measures of trading activity at different investment horizons are introduced through scaling of variance of the underlying processes. On the three most liquid US indices - DJI, NASDAQ and S&P500 - we show that predictions of fractal markets hypothesis actually fit the observed behavior quite well.Comment: 11 pages, 3 figure

Removing Barriers, Integrating Research, Spreading Excellence: The European Satellite Communications Network of Excellence "SatNEx"

Within the recently launched 6th Research Framework Programme of the European Commission, 21 major players in satellite communications research have joined forces to implement the European Satellite Communications Network of Excellence (SatNEx). The primary goal of SatNEx is to achieve long-lasting integration of the European research in satellite communication and to develop a common base of knowledge, thus contributing to the realization of the European Research Area. This paper discusses the background and motivation for implementation of the network and highlights the SatNEx mission and key objectives. A top-level overview is then provided including a description of the consortium, the Joint Programme of Activities (JPA) and the time schedule with deliverables and milestones. Finally, an update of ongoing work is presented

Negative symptoms as key features of depression among cannabis users: a preliminary report.

OBJECTIVE: Cannabis use is frequent among depressed patients and may lead to the so-called "amotivational syndrome", which combines symptoms of affective flattening and loss of emotional reactivity (i.e. the so-called "negative" symptomatology). The aim of this study was to investigate the negative symptomatology in depressed patients with concomitant cannabis use disorders (CUDs) in comparison with depressed patients without CUDs. PATIENTS AND METHODS: Fifty-one patients with a diagnosis of Major Depressive Disorder (MDD) and concomitant CUD and fifty-one MDD patients were enrolled in the study. The 21-Item Hamilton Depression Rating Scale (HDRS) and the negative symptoms subscales of the Positive and Negative Syndrome Scale (PANSS) were used to assess depressive and negative symptomatology. RESULTS: Patients with cannabis use disorders presented significantly more severe negative symptoms in comparison with patients without cannabis use (15.18 ± 2.25 vs 13.75 ± 2.44; t100 = 3.25 p = 0.002). DISCUSSION: A deeper knowledge of the "negative" psychopathological profile of MDD patients who use cannabis may lead to novel etiopathogenetic models of MDD and to more appropriate treatment approaches

Handover procedures in integrated satellite and terrestrial mobile systems

The integration of satellite and terrestrial mobile systems is investigated in terms of the strategies for handover across the integrated cellular coverage. The handover procedure is subdivided into an initialization phase, where the need for issuing a handover request must be identified, and an execution phase, where the request must be satisfied, if possible, according to a certain channel assignment strategy. A modeling approach that allows the design of the parameters that influence the performance of the overall handover procedure is presented, along with a few numerical results

Bipolar polaron pair recombination in P3HT/PCBM solar cells

The unique properties of organic semiconductors make them versatile base materials for many applications ranging from light emitting diodes to transistors. The low spin-orbit coupling typical for carbon-based materials and the resulting long spin lifetimes give rise to a large influence of the electron spin on charge transport which can be exploited in spintronic devices or to improve solar cell efficiencies. Magnetic resonance techniques are particularly helpful to elucidate the microscopic structure of paramagnetic states in semiconductors as well as the transport processes they are involved in. However, in organic devices the nature of the dominant spin-dependent processes is still subject to considerable debate. Using multi-frequency pulsed electrically detected magnetic resonance (pEDMR), we show that the spin-dependent response of P3HT/PCBM solar cells at low temperatures is governed by bipolar polaron pair recombination involving the positive and negative polarons in P3HT and PCBM, respectively, thus excluding a unipolar bipolaron formation as the main contribution to the spin-dependent charge transfer in this temperature regime. Moreover the polaron-polaron coupling strength and the recombination times of polaron pairs with parallel and antiparallel spins are determined. Our results demonstrate that the pEDMR pulse sequences recently developed for inorganic semiconductor devices can very successfully be transferred to the study of spin and charge transport in organic semiconductors, in particular when the different polarons can be distinguished spectrally

Assessing the Feasibility of MaaS. A Contribution from Three Italian Case Studies

Making all types of public and private transport services available to users through a single and integrated digital platform is the new urban mobility paradigm called Mobility as a Service (MaaS). This scheme allows both a more sustainable urban transportation system and a more effi-cient transport service for users. For MaaS to be successful, its implementation should adapt to the specific features of the location covered by the service. The city maturity level has to be considered in terms of multimodality, infrastructures, regulations, user goals, and user willingness to use and pay for MaaS services. This paper discusses and analyses the results of a survey on MaaS con-ducted in three Italian metropolitan areas: Turin, Rome, and Genoa, which have very different and specific characteristics. The comparative analysis enables the definition of drivers, obstacles, and requisites for MaaS implementation to be successful. When it comes to cities with conservative mobility policies or cities that are new to MaaS experiences, resistance to adoption of the service might occur. The results of the research discussed in this paper can be a useful resource to enable decision makers to develop more effective and efficient transportation policies

Use of the breeding technique to estimate the structure of the analysis 'errors of the day'

A 3D-variational data assimilation scheme for a quasi-geostrophic channel model (Morss, 1998) is used to study the structure of the background error and its relationship to the corresponding bred vectors. The "true" evolution of the model atmosphere is defined by an integration of the model and "rawinsonde observations" are simulated by randomly perturbing the true state at fixed locations. Case studies using different observational densities are considered to compare the evolution of the Bred Vectors to the spatial structure of the background error. In addition, the bred vector dimension (BV-dimension), defined by Patil et al. (2001) is applied to the bred vectors. It is found that after 3-5 days the bred vectors develop well organized structures which are very similar for the two different norms (enstrophy and streamfunction) considered in this paper. When 10 surrogate bred vectors (corresponding to different days from that of the background error) are used to describe the local patterns of the background error, the explained variance is quite high, about 85-88%, indicating that the statistical average properties of the bred vectors represent well those of the background error. However, a subspace of 10 bred vectors corresponding to the time of the background error increased the percentage of explained variance to 96-98%, with the largest percentage when the background errors are large. These results suggest that a statistical basis of bred vectors collected over time can be used to create an effective constant background error covariance for data assimilation with 3D-Var. Including the "errors of the day" through the use of bred vectors corresponding to the background forecast time can bring an additional significant improvement