Experimental Studies on the Effect of Antenna Orientations to the Performance of OFDM-based System

Software-defined radio (SDR) is an emerging and promising high re-configurable platform for rapid prototyping inreal environment applications. It offers both flexibility and low cost to facilitate the development process of agile communication system, such as Orthogonal Frequency Division Multiplexing (OFDM). Other than modulation and transmission technique like OFDM, antenna orientations play a significant importance in wireless communication. The availabililty of SDR platform like USRP has enabled the empirical evaluation of antenna orientation to the system performance. The performance has been evaluated in terms of throughput and packet error rate. The findings show the antenna orientation affect the system performance significantly

Performance Evaluation of Energy Detector Based Spectrum Sensing for Cognitive Radio using NI USRP-2930

This paper presents the performance evaluation of the Energy Detector technique, which is one of the most popular Spectrum Sensing (SS) technique for Cognitive Radio (CR). SS is the ability to detect the presence of a Primary User (PU) (i.e. licensed user) in order to allow a Secondary User (SU) (i.e unlicensed user) to access PU's frequency band using CR, so that the available frequency bands can be used efficiently. We used for implementation an Universal Software Radio Peripheral (USRP), which is the most used Software Defined Radio (SDR) device for research in wireless communications. Experimental measurements show that the Energy Detector can obtain good performances in low Signal to Noise Ratio (SNR) values. Furthermore, computer simulations using MATLAB are closer to those of USRP measurements

Evaluación de desempeño de los estimadores de desplazamiento de frecuencia de portadora en sistemas variantes en el tiempo

Resumen: Una evaluación del desempeño de los algoritmos de estimación del desplazamiento de la frecuencia de portadora (CFO) es presentado para sistemas OFDM bajo la suposición de variabilidad temporal del canal de comunicación. Típicamente, dichos algoritmos se basan en el propuesto por Timothy Schmidl y Donald Cox, el cual a partir de una secuencia entrenamiento y considerando invariabilidad del canal lleva a cabo la sincronización de trama y la estimación del CFO, aproximándose al límite inferior de Cramér-Rao. La evaluación del desempeño se llevó acabo considerando ambientes con diversas relaciones señal a ruido (SNR) y diferentes frecuencias Doppler (FD). De los resultados obtenidos se ha podido corroborar que el error cuadrático medio de la estimación del CFO suponiendo una sincronización en tiempo perfecta, se incrementa a medidaque el canal se vuelve más variante en el tiempo. Lo cual da pie a la búsqueda de nuevas técnicas de estimación y corrección del CFO para canales variantes en el tiempo. Palabras Clave: OFDM, canal variante en el tiempo, CFO

Una Revisión Sistemática en los Marcos de Trabajo de Desarrollo Software en las MiPyMEs Productoras de Software

Resumen: Una revisión sistemática es considerada como un método o protocolo que permite sintetizar investigaciones científicas de diversas áreas, la Ingeniería de Software no es la excepción. En este artículo se presenta este protocolo aplicado en la búsqueda de publicaciones relacionadas con las adaptaciones a los marcos de trabajo de desarrollo de software llevadas a cabo en MiPyMEs desarrolladoras de software, en el período comprendido de 1995 al 2013, centrándose en tendencias, países y sectores que publican; así como en los modelos, metodologías, estándares, procesos técnicos, procesos de implementación y procesos de reúso del software. Los resultados obtenidos muestran que los países con mayor número de publicaciones sobre el tópico seleccionado son Estados Unidos y Reino Unido, que en su conjunto suman 21%; y que otros países suman el 79% restante. Se observa que el sector con mayor número de publicaciones es el sector educativo con 76%, seguido por los centros de investigación con 18% y el sector privado con el 6%. El modelo de procesos y la metodología más utilizados son CMMi con 33% e IDEAL con 22%, respectivamente. Los estándares más utilizados, con el 18% cada uno, son el ISO/IEC 15504 y CORBA; y los procesos del ciclo de vida del software mayormente abordados son: análisis de requisitos del sistema con un 33% y construcción con un 29%. Palabras Clave: MiPyME, revisión sistemática, modelos, metodologías, estándares de desarrollo de software, procesos técnicos, procesos de implementación, procesos de reúso del software

An OFDM Signal Identification Method for Wireless Communications Systems

Distinction of OFDM signals from single carrier signals is highly important for adaptive receiver algorithms and signal identification applications. OFDM signals exhibit Gaussian characteristics in time domain and fourth order cumulants of Gaussian distributed signals vanish in contrary to the cumulants of other signals. Thus fourth order cumulants can be utilized for OFDM signal identification. In this paper, first, formulations of the estimates of the fourth order cumulants for OFDM signals are provided. Then it is shown these estimates are affected significantly from the wireless channel impairments, frequency offset, phase offset and sampling mismatch. To overcome these problems, a general chi-square constant false alarm rate Gaussianity test which employs estimates of cumulants and their covariances is adapted to the specific case of wireless OFDM signals. Estimation of the covariance matrix of the fourth order cumulants are greatly simplified peculiar to the OFDM signals. A measurement setup is developed to analyze the performance of the identification method and for comparison purposes. A parametric measurement analysis is provided depending on modulation order, signal to noise ratio, number of symbols, and degree of freedom of the underlying test. The proposed method outperforms statistical tests which are based on fixed thresholds or empirical values, while a priori information requirement and complexity of the proposed method are lower than the coherent identification techniques

Three-Event Energy Detection with Adaptive Threshold for Spectrum Sensing in Cognitive Radio Systems

Implementation of dynamic spectrum access (DSA) in cognitive radio (CR) systems requires the unlicensed secondary users (SU) to implement spectrum sensing to monitor the activity of the licensed primary users (PU). Energy detection (ED) is one of the most widely used methods for spectrum sensing in CR systems, and in this paper we present a novel ED algorithm with an adaptive sensing threshold. The three-event ED (3EED) algorithm for spectrum sensing is considered for which an accurate approximation of the optimal decision threshold that minimizes the decision error probability (DEP) is found using Newton’s method with forced convergence in one iteration. The proposed algorithm is analyzed and illustrated with numerical results obtained from simulations that closely match the theoretical results and show that it outperforms the conventional ED (CED) algorithm for spectrum sensing

Detection of OFDM Signals Using Pilot Tones and Applications to Spectrum Sensing for Cognitive Radio Systems

Nowadays there are an increasing number of wireless devices which support wireless networking and the need for higher data rate communication is increasing rabidly. As more and more systems go wireless, approaching technologies will face spectral crowding and existence of wireless devices will be an important issue. Because of the limited bandwidth availability, accepting the request for higher capacity and data rates is a challenging task, demanding advanced technologies that can offers new methods of using the available radio spectrum. Cognitive radio introduces a key solution to the spectral increasing issue by presenting the opportunistic usage of spectrum that is not heavily occupied by licensed users. It is a latest idea in wireless communications systems which objective to have more adaptive and aware communication devices which can make better use of available natural resources. Cognitive radio appears to be an attractive solution to the spectral congestion problem by introducing the notion of opportunistic spectrum use. Cognitive radios can operate as a secondary systems on top of existence system which are called primary (or licensed) systems. In this case, secondary (cognitive) users need to detect the unused spectrum in order to be able to access it. Because of its many advantages, orthogonal frequency division multiplexing (OFDM) has been successfully used in numerous wireless standards and technologies. It\u27s shown that OFDM will play an important role in realizing the cognitive radio concept as well by providing a proven, scalable, and adaptive technology for air interface. Researches show that OFDM technique is considered as a candidate for cognitive radio systems. The objective of this dissertation is to explore detecting of OFDM modulated signals using pilot tones information. Specifically we applying Time-Domain Symbol Cross-Correlation (TDSC) method in the confect of actual 4G wireless standards such as WIMAX and LTE. This detection is only based upon the knowledge of pilot structures without knowledge of received signal so that, it can be performed on every portion of the received signal. The approach induces Cross-Correlation between pilots subcarriers and exploits the deterministic and periodic characteristics of pilot mapping in the time frequency domain