Bandwidth compression of noisy signals with square-wave subcarrier

This article discusses a method for downconverting the square-wave subcarrier of spacecraft signals, such as the one from Galileo, which results in a compression bandwidth that lowers the sample rate significantly. The study is focused on three issues. The first is the selection of an adequate down-mixing signal for the resulting signal to have a format similar to that of the original signal, except at a lower subcarrier frequency. The second is the control of the noise level so that the signal to noise ratio is not degraded due to the downconversion. The third is to determine the bandwidth of the downconverted signal considering the uncertainty of the residual carrier frequency

Symbol signal-to-noise ratio loss in square-wave subcarrier downconversion

This article presents the simulated results of the signal-to-noise ratio (SNR) loss in the process of a square-wave subcarrier down conversion. In a previous article, the SNR degradation was evaluated at the output of the down converter based on the signal and noise power change. Unlike in the previous article, the SNR loss is defined here as the difference between the actual and theoretical symbol SNR's for the same symbol-error rate at the output of the symbol matched filter. The results show that an average SNR loss of 0.3 dB can be achieved with tenth-order infinite impulse response (IIR) filters. This loss is a 0.2-dB increase over the SNR degradation in the previous analysis where neither the signal distortion nor the symbol detector was considered

SNR degradation in square-wave subcarrier downconversion

This article presents a study of signal-to-noise ratio (SNR) degradation in the process of square-wave subcarrier downconversion. The study shows three factors that contribute to the SNR degradation: the cutoff of the higher frequency components in the data, the approximation of a square wave with a finite number of harmonics, and nonideal filtering. Both analytical and simulation results are presented

Constructions of Large Graphs on Surfaces

We consider the degree/diameter problem for graphs embedded in a surface, namely, given a surface $\Sigma$ and integers $\Delta$ and $k$, determine the maximum order $N(\Delta,k,\Sigma)$ of a graph embeddable in $\Sigma$ with maximum degree $\Delta$ and diameter $k$. We introduce a number of constructions which produce many new largest known planar and toroidal graphs. We record all these graphs in the available tables of largest known graphs. Given a surface $\Sigma$ of Euler genus $g$ and an odd diameter $k$, the current best asymptotic lower bound for $N(\Delta,k,\Sigma)$ is given by $$\sqrt{\frac{3}{8}g}\Delta^{\lfloor k/2\rfloor}.$$ Our constructions produce new graphs of order \begin{cases}6\Delta^{\lfloor k/2\rfloor}& \text{if $\Sigma$ is the Klein bottle}\\ \(\frac{7}{2}+\sqrt{6g+\frac{1}{4}}\)\Delta^{\lfloor k/2\rfloor}& \text{otherwise,}\end{cases} thus improving the former value by a factor of 4.Comment: 15 pages, 7 figure

On large bipartite graphs of diameter 3

We consider the bipartite version of the {\it degree/diameter problem}, namely, given natural numbers $d\ge2$ and $D\ge2$, find the maximum number $\N^b(d,D)$ of vertices in a bipartite graph of maximum degree $d$ and diameter $D$. In this context, the bipartite Moore bound \M^b(d,D) represents a general upper bound for $\N^b(d,D)$. Bipartite graphs of order \M^b(d,D) are very rare, and determining $\N^b(d,D)$ still remains an open problem for most $(d,D)$ pairs. This paper is a follow-up to our earlier paper \cite{FPV12}, where a study on bipartite $(d,D,-4)$-graphs (that is, bipartite graphs of order \M^b(d,D)-4) was carried out. Here we first present some structural properties of bipartite $(d,3,-4)$-graphs, and later prove there are no bipartite $(7,3,-4)$-graphs. This result implies that the known bipartite $(7,3,-6)$-graph is optimal, and therefore $\N^b(7,3)=80$. Our approach also bears a proof of the uniqueness of the known bipartite $(5,3,-4)$-graph, and the non-existence of bipartite $(6,3,-4)$-graphs. In addition, we discover three new largest known bipartite (and also vertex-transitive) graphs of degree 11, diameter 3 and order 190, result which improves by 4 vertices the previous lower bound for $\N^b(11,3)$

Applying stress-testing on value at risk (VaR) methodologies

In recent years, Value at Risk (VaR) methodologies, i. e., Parametric VaR, Historical Simulation and the Monte Carlo Simulation have experienced spectacular growth within the new regulatory framework which is Basle II. Moreover, complementary analyses such a Stress-testing and Back-testing have also demonstrated their usefulness for financial risk managers. In this paper, we develop an empirical Stress-Testing exercise by using two historical scenarios of crisis. In particular, we analyze the impact of the 11-S attacks (2001) and the Latin America crisis (2002) on the level of risk, previously calculated by different statistical methods. Consequently, we have selected a Spanish stock portfolio in order to focus on market risk

Humanizar las TIC:Reflexiones desde América Latina sobre la Sociedad de la Información

Es fa una breu descripció de la realitat de les TIC en l’actual societat del coneixement, especialment en els païsosen desenvolupament, a partir de les conclusions de la darrera Cimera Mundial de la Societat de la Informació (CMSI). Es comparen les dades oficials presentades a la trobada amb la realitat d’Amèrica Llatina i els esforços realitzats a Mèxic per evitar el trencament digital i com a primer pas per a humanitzar les TIC. Es repassa el rol de les biblioteques en la societat de la informació a partir del Manifest d’Alexandria sobre biblioteques i s’exposa l’ampli treball fet a la Universidad de Colima, Centre UNESCO a Mèxic, com a  referent llatinoamericà en l’àmbit de les TIC. S’inclou un annex sobre temes clau extrets de l’informe Cap a les societats del coneixement presentat a la cimera i una relació de dades i xifres que documenten el treball.A brief description of the reality of TICs is made in the present information knowledge society, especially in developing countries, from the conclusions of the last World-wide Summit of the Information Society (CMSI). The official data presented in the encounter are compared with the reality of Latin America and the efforts made in Mexico to avoid the digital breach as a first step to humanize the TIC.The role of libraries in the society of information is reviewed from Manifesto of Alexandria on the libraries and the extensive work made in the University of Colima, UNESCO Center in Mexico, as a Latin American referent in TICs. It includes an annex on key subjects extracted of the report «Towards the societies of knowledge»  presented in thesummit and a relation of data and numbers that document the work.Se realiza una breve descripción de la realidad de las TIC en la actual sociedad del conocimiento, especialmente en los países en desarrollo, a partir de las conclusiones de la última Cumbre Mundial de la Sociedadde la Información (CMSI). Se comparan los datos oficiales presentados en el encuentro con la realidad de América Latina y los esfuerzos realizados en México para evitar la brecha digital como primer paso para humanizar las TIC. Se repasa el papel de las bibliotecas en la sociedad de la información a partir del Manifiesto de Alejandría sobre las bibliotecas y se expone el extenso trabajo realizado en la Universidad de Colima, Centro UNESCO en México, como referente latinoamericano en el ámbito de las TIC. Incluye un anexo sobre temas clave extraídos del informe Hacia las sociedades del conocimiento presentado en la cumbre  y una relación de datos y cifras que documentan el trabajo