Fabio G. Guerrero

Vertical Handoff Algorithms — A new approach for performance evaluation

A myriad of Vertical Handoff Algorithms (VHA) have been proposed by researchers and networks practitioners. These algorithms allow mobile terminals (MT) to maintain the network connection when they switch from one wireless network to another one. Given the amount of proposed VHA and the need for an objective assessment of these solutions different evaluation methodologies have been proposed, becoming the problem of evaluation of VHA in an interesting challenge. However, there is no consensus on how to evaluate performance of VHA. In this paper, we address this issue by proposing a new approach for evaluating the VHA, which is based on multi-criteria evaluation and criticality analysis — a specific concept taken from the operational reliability. The new approach allows evaluating VHA using measured values of some defined parameters, which can be obtained from simulating VHA on a network simulation tool (e. g. NCTUns, NS −2, OMNET++, among others) or generic software simulation tools (e.g. MATLAB). As a test of the new model, an evaluation of five VHA is presented.

Performance evaluation of Vertical Handoff Algorithms

Different Vertical Handoff Algorithms (VHA) have been proposed in the literature recently. However, there is no consensus on how to evaluate performance of different VHA at the research community. Although some models have been proposed for evaluation of the VHA, this issue is a challenge because the VHA have evolved to become more sophisticated, thus the evaluation models must consider a variety of parameters. In this paper, we propose a new evaluation model for VHA that has been designed based on specific concepts taken from the multi-criteria evaluation and operational reliability. The proposed evaluation model allows analyzing VHA using measured values of some defined parameters, which can be obtained from simulating VHA on a network simulation tool. We present as a case study an evaluation of two VHA that shows the new model functionality and results.

Stochastic Traffic Analysis of Contemporary Internet High-Speed Links

The aim of this paper is to provide a better understanding of the stochastic properties of contemporary Internet traffic. Previous known studies on Internet Traffic are based on samples captured several years ago, where both Internet’s applications and user behavior were quite different from today’s world. In this paper, a stochastic traffic analysis of contemporary Internet traffic seen on high-speed backbone links, where the size of the analyzed samples amounts to the billions of packets, is presented. The probability distribution functions of packet inter-arrival time, number of packets per unit of time, and average packet length were both calculated and analyzed. A wide sense stationarity test for the observed traffic was performed on several time scales. In order to analyze the self-similarity properties of the process, the Hurst index, obtained through the wavelet transform method, was employed. Finally, decimation used a useful auxiliary technique in the process of scale invariance analysis is presented.

Aplicación web basada en programación por restricciones para ingeniería de asignación de espectro

espanolLa flexibilidad de uso del espectro radioelectrico que requieren los paradigmas emergentes, la demanda del espectro radioelectrico impulsada por las nuevas tecnologias inalambricas, las nuevas aplicaciones y las politicas gubernamentales orientadas a la masificacion del uso de Internet, requieren que las autoridades administradoras del espectro cuenten con herramientas cada vez mas inteligentes para hacer su labor de forma eficiente. En este trabajo se presenta el diseno e implementacion de una aplicacion web de ayuda a las actividades de gestion del espectro radioelectrico usando programacion por restricciones. El diseno incluye un modelo matematico de restricciones de asignacion, un modelo matematico de restricciones para interferencias, una base de datos relacional del Cuadro Nacional de Atribucion de Bandas de Frecuencia considerando bandas, canales y servicios asociados a la division geopolitica de Colombia, y una base de datos de asignacion de operadores. La herramienta permite crear y parametrizar diferentes niveles de restricciones estableciendo diferentes criterios y pesos de costos. En el modulo de analisis de interferencias se tiene en cuenta la ubicacion geografica y las caracteristicas tecnicas de las estaciones transmisoras. La herramienta desarrollada en este trabajo puede ser de utilidad, entre otros, en estudios de optimizacion de asignacion, valoracion de politicas de reasignacion de espectro, analisis de asignacion para maximizar criterios especificos, reduccion de costos tecnologicos de implementacion de tecnologias especificas y ayudar a identificar variables objetivas en la estimacion del precio del espectro. Para facilitar la comprension y explotacion de la aplicacion se incluyen varios ejemplos de caracter didactico. EnglishThe flexibility of spectrum usage required by emerging paradigms, radio spectrum demand driven by new wireless technologies, new applications and government policies oriented to massive use of Internet require spectrum management authorities to have smarter tools to do their work in an efficient way. This paper presents the design and implementation of a web application to support spectrum management activities using constraints programming. The design includes a mathematical model for allocation constraints, a mathematical model for interference constraints, a relational database of the National Allocation Table considering bands, channels and services associated with geopolitical division of Colombia, and an operator allocation database. These tools allow creating and to parameterize different levels of restrictions establishing different costs and weights. The interference analysis module takes into account the geographical location and technical characteristics of transmitting stations. The tool developed in this work can be used, among others, in allocation optimization studies, assessing policies of spectrum reallocation, allocation analysis to maximize specific criteria, reducing technology costs of implementing specific technologies and help identifying objective variables for spectrum price estimation. To facilitate the understanding and exploitation of the application several didactic examples are included.