The effects of controlling capture on multimedia traffic for shared Ethernet systems

The IEEE 802.3 Ethernet standard is evolving to support much higher data rates and improved quality of service. Even low cost halfduplex CSMA/CD networks can be improved using an enhanced backwardscompatible collision arbitration algorithm known as the Binary Logarithmic Arbitration Method (BLAM) now being proposed as the IEEE 802.3w draft standard. BLAM is designed to coexist fairly with the existing Binary Exponential Backoff (BEB) algorithm, while eliminating its shortterm unfairness problems. In this paper, we focus on how BLAM improves Ethernet performance for multimedia data transport. Analytical, simulation, and prototype hardware experimental results using synthetic, trace, and actual measured traffic are presented. It is shown that BLAM Ethernets can support significantly greater numbers of video streams than existing BEB Ethernets and if the delivery requirements for the video traffic are not too strict, that BLAM Ethernets can even support video if the network is completely saturated with data traffic.     

Fabrication,characterization, and analysis of photodetectors metal-porous silicon with different geometry and thickness of the porous silicon layer

Porous silicon photodetectors obtained by electrochemical etching of p-type non-polished crystalline silicon were studied. A metal-porous silicon structure was used to obtain the rectifying behavior. The geometry of the metal layer deposited by thermal evaporation on the porous zone was modified with different masks fabricated using a photolithographic method. The samples obtained under different anodization conditions were characterized by PL. The sample that showed the best intensity in photoluminescence, centered on 675 nm, was selected and five samples obtained under these conditions were prepared to compare the difference in the photoresponse because of the geometry of the evaporated metal layer. The responsivities obtained show us an important difference between the devices and allow us to propose a specific geometrical pattern to obtain a better response in this kind of devices.     

Fault Detection in Switched Current Circuits Using Built-in Transient Current Sensors

Switched current (SI) circuits use analogue memory cells as building blocks. In these cells, like in most analogue circuits, there are hard-to-detect faults with conventional test methods. A test approach based on a built-in dynamic current sensor (BIDCS), whose detection method weights the highest frequency components of the dynamic supply current of the circuit under test, makes possible the detection of these faults, taking into account the changes in the slope of the dynamic supply current induced by the fault. A study of the influence of these faults in neighbouring cells helps to minimize the number of BICS needed in SI circuits as is shown in two algorithmic analogue-to-digital converters. Yolanda Lechuga received a degree in Industrial Engineering from the University of Cantabria (Spain) in April 2000. Since then, she has been collaborating with the Microelectronics Engineering Group at the University of Cantabria, in the Electronics Technology, Systems and Automation Engineering Department. Since October 2000 she has been a post-graduate student, to be appointed as lecturer at this university, where she is working in her Ph.D. She is interested in supply current test methods, fault simulation, BIST and design for test of mixed signal integrated circuits. Román Mozuelos received a degree in Physics with electronics from the University of Cantabria, Spain. From 1991 to 1995 he was working on the development of quartz crystal oscillators. Currently, he is a Ph.D. student and an assistant teacher at the University of Cantabria in the Department of Electronics Technology. His interests include mixed-signal design and test, fault simulation, and supply current monitoring. Miguel A. Allende received his graduate degree in 1985 and Ph.D. degree in 1994, both from the University of Cantabria, Santander, Spain. In 1996, he became an Assistant Professor of Electronics Technology at the same Institution, where he is a member of the Microelectronics Engineering Group at the Electronics Technology, Systems and Automation Engineering Department in the Industrial and Telecommunication Engineering School. His research interests include design of VLSI circuits for industrial applications, test and DfT in digital VLSI communication circuits, and power supply current test of mixed, analogue and digital circuits. Mar Martínez received her graduate degree and Ph.D. from the University of Cantabria (Spain) in 1986 and 1990. She has been Assistant Professor of Electronic Technology at the University of Cantabria (Spain) since 1991. At present, she is a member of the Electronics Technology, Systems and Automation Engineering Department in the Industrial and Telecommunication Engineering School. She has participated in several EU and Spanish National Research Projects. Her main research interest is mixed, analogue and digital circuit testing, using techniques based on supply current monitoring. She is also interested in test and design for test in digital VLSI circuits. Salvador Bracho obtained his graduate degree and Ph.D. from the University of Seville (Spain) in 1967 and 1970. He was appointed Professor of Electronic Technology at the University of Cantabria (Spain) in 1973, where, at present, he is a member of the Electronics Technology, Systems and Automation Engineering Department in the Industrial and Telecommunication Engineering School. He has participated, as leader of the Microelectronics Engineering Group at the University of Cantabria, in more than twenty EU and Spanish National Research Projects. His primary research interest is in the area of test and design for test, such as full scan, partial scan or self-test techniques in digital VLSI communication circuits. He is also interested in mixed-signal, analogue and digital test, using methods based on power supply current monitoring. Another research interest is the design of analogue and digital VLSI circuits for industrial applications. Prof. Bracho is a member of the Institute of Electrical and Electronic Engineers.     

Game theory and time utility functions for a radio aware scheduling algorithm for WiMAX networks

In WiMAX systems the Base Station scheduler plays a key role as it controls the sharing of the radio resources among the users. The goal of the scheduler is multiple: achieve fair usage of the resources, satisfy the QoS requirements of the users, maximize goodput, and minimize power consumption, and at the same time ensuring feasible algorithm complexity and system scalability. Since most of these goals are contrasting, scheduler designers usually focus their attention on optimizing one aspect only. In this scenario, we propose a scheduling algorithm (called GTS_Nmathrm{GTS_N}) whose goal is to contemporaneously achieve efficiency and fairness, while also taking into account the QoS requirements and the channel state. GTS_Nmathrm{GTS_N} exploits the properties of Time Utility Functions (TUFs) and Game Theory. Simulations prove that the performance of GTS_N,mathrm{GTS_N}, when compared to that of several well-known schedulers, is remarkable. GTS_Nmathrm{GTS_N} provides the best compromise between the two contrasting objectives of fairness and efficiency, while QoS requirements are in most cases guaranteed. However, the exponential complexity introduced by the game theory technique makes it rather impractical and not computationally scalable for a large number of users. Thus we developed a suboptimal version, named sub-GTS_N.mathrm{GTS_N}. We show that this version retains most of the features and performance figures of its brother, but its complexity is linear with the number of users.     

Dosage individualization of erythropoietin using a profile-dependent support vector regression

The external administration of recombinant human erythropoietin is the chosen treatment for those patients with secondary anemia due to chronic renal failure in periodic hemodialysis. The objective of this paper is to carry out an individualized prediction of the EPO dosage to be administered to those patients. The high cost of this medication, its side-effects and the phenomenon of potential resistance which some individuals suffer all justify the need for a model which is capable of optimizing dosage individualization. A group of 110 patients and several patient factors were used to develop the models. The support vector regressor (SVR) is benchmarked with the classical multilayer perceptron (MLP) and the Autoregressive Conditional Heteroskedasticity (ARCH) model. We introduce a priori knowledge by relaxing or tightening the epsilon-insensitive region and the penalization parameter depending on the time period of the patients' follow-up. The so-called profile-dependent SVR (PD-SVR) improves results of the standard SVR method and the MLP. We perform sensitivity analysis on the MLP and inspect the distribution of the support vectors in the input and feature spaces in order to gain knowledge about the problem.     

Room Temperature Spin-Phonon Coupling in Cr2O3 Nanocrystals

In this study, nanocrystals of antiferromagnetic Cr₂O₃ are shown via Raman spectroscopy to display peculiar lattice dynamics in terms of phonon softening and the occurrence of an exceptionally strong spin-phonon coupling. This effect, which is observed to persist well above the onset of the antiferromagnetic ordering temperature, is ascribed to locally correlated spin fluctuations due to the modulation of the magnetic exchange interactions as the chromium atoms oscillate about their equilibrium position. It is found that the spin-phonon coupling strength is governed by the competing antiferromagnetic and ferromagnetic interactions, where changes in the surface spin configuration can also play a crucial role. Overall, this work proves the size dependence of the interplay between the crystalline and magnetic structures in 3D antiferromagnets varying the surface-to-volume ratio and helps establish the fundamentals for a spin-phonon coupling engineering at the nanoscale via a simple route in a very stable and easy to synthesize material. More importantly, it demonstrates the possibility of coupling phononic excitations with the magnetization dynamics at room temperature, offering a highly prospective nanomaterial for the design of novel magnonic devices.     

Secure Distributed Key Generation for Discrete-Log Based Cryptosystems

A Distributed Key Generation (DKG) protocol is an essential component of threshold cryptosystems required to initialize the cryptosystem securely and generate its private and public keys. In the case of discrete-log-based (dlog-based) threshold signature schemes (ElGamal and its derivatives), the DKG protocol is further used in the distributed signature generation phase to generate one-time signature randomizers (r = g^k). In this paper we show that a widely used dlog-based DKG protocol suggested by Pedersen does not guarantee a uniformly random distribution of generated keys: we describe an efficient active attacker controlling a small number of parties which successfully biases the values of the generated keys away from uniform. We then present a new DKG protocol for the setting of dlog-based cryptosystems which we prove to satisfy the security requirements from DKG protocols and, in particular, it ensures a uniform distribution of the generated keys. The new protocol can be used as a secure replacement for the many applications of Pedersen's protocol. Motivated by the fact that the new DKG protocol incurs additional communication cost relative to Pedersen's original protocol, we investigate whether the latter can be used in specific applications which require relaxed security properties from the DKG protocol. We answer this question affirmatively by showing that Pedersen's protocol suffices for the secure implementation of certain threshold cryptosystems whose security can be reduced to the hardness of the discrete logarithm problem. In particular, we show Pedersen's DKG to be sufficient for the construction of a threshold Schnorr signature scheme. Finally, we observe an interesting trade-off between security (reductions), computation, and communication that arises when comparing Pedersen's DKG protocol with ours.     

Model-Based Detection of Heart Rate Turbulence Using Mean Shape Information

A generalized likelihood ratio test (GLRT) statistic is proposed for detection of heart rate turbulence (HRT), where a set of Karhunen–LoÈve basis functions models HRT. The detector structure is based on the extended integral pulse frequency modulation model that accounts for the presence of ectopic beats and HRT. This new test statistic takes a priori information regarding HRT shape into account, whereas our previously presented GLRT detector relied solely on the energy contained in the signal subspace. The spectral relationship between heart rate variability (HRV) and HRT is investigated for the purpose of modeling HRV “noise” present during the turbulence period, the results suggesting that the white noise assumption is feasible to pursue. The performance was studied for both simulated and real data, leading to results which show that the new GLRT detector is superior to the original one as well as to the commonly used parameter turbulence slope (TS) on both types of data. Averaging ten ventricular ectopic beats, the estimated detection probability of the new detector, the previous detector, and TS were found to be 0.83, 0.35, and 0.41, respectively, when the false alarm probability was held fixed at 0.1.