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This paper presents the development and evaluation of two linear algorithms for forecasting reception power for different channels at an assigned spectrum band of global systems for mobile communications (GSM), in order to analyze the spatial opportunity for reuse of frequencies by secondary users (SUs) in a cognitive radio (CR) network. The algorithms employed correspond to seasonal autoregressive integrated moving average (SARIMA) and generalized autoregressive conditional heteroskedasticity (GARCH), which allow for a forecast of channel occupancy status. Results are evaluated using the following criteria: availability and occupancy time for channels, different types of mean absolute error, and observation time. The contributions of this work include a more integral forecast as the algorithm not only forecasts reception power but also the occupancy and availability time of a channel to determine its precision percentage during the use by primary users (PUs) and SUs within a CR system. Algorithm analyses demonstrate a better performance for SARIMA over GARCH algorithm in most of the evaluated variables.

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This paper presents the modeling and simulation of a Very High Frequency Data Link Mode 2 (VDL2) sub network to support Controller Pilot Data Link Communication (CPDLC), at El Dorado International Airport in Bogota City. The modeling and simulation were made in order to determine performance characteristics and determine if VDL2 could meet future traffic load increase. The simulation was performed using Network Simulator 2 (NS2). An overview of the technologies currently used for air-ground communication in Colombia ispresented. Also this paper shows a glimpse of the features of the VDL Mode 2 protocol and CPDLC service. The VDL Mode 2 subnet model and the subsequent simulation were derived from the characteristics of Colombian airspace and air traffic conditions in the Bogota Terminal Area (TMA). Finally, the simulation results are presented.

ResumenEn este trabajo se hace un examen del comportamiento de la proporción de rechazos equivocados de la hipótesis nula (error tipo I) en condiciones plenas de aplicabilidad de la distribución t de Student, es decir, con variables independientes cuya distribución es normal tanto bajo el supuesto de homogeneidad de varianzas como en las condiciones de heterocedasticidad.Palabras clave: estadística t, prueba t, monotonía, estabilidad, prueba de WelchSatterwhaite. AbstractIn this paper we review the behavior of the type I error rate of Student's t-test and Welch-Sattetthwaite test for comparing two means with independent samples from normal populations under the assumption of homogeneity of variances and under conditions of heteroscedasticity. The results, obtained by the Monte Carlo method show the Welch-Satterthwaite well behaved in all cases.