Pseudorandom Sequences in Spread-Spectrum Communications Generated by Cellular Automata

 

F.C. Ordaz-Salazar¹, J.S. González-Salas*¹, E. Campos-Cantón², H.C. Rosu²

 

¹ Universidad Politécnica de San Luis Potosí, San Luis Potosí, S.L.P. México *jsgs100573@hotmail.com.

² Instituto Potosino de Investigación Científica y Tecnológica, San Luis Potosí, S.L.P., México.

 

Abstract

Dynamical systems methods have been recently used in spread-spectrum digital communication systems. The expansion of the spectrum using a pseudorandom sequence with a higher frequency than the information signal is the key feature for its robustness against the signal traveling interference through the channel. In this work, we propose to generate pseudorandom sequences by employing cellular automata and we check these sequences have the necessary properties which are required in modern communication systems. The computed sequences obtained by the cellular automata are tested in a quadrature phase shift keying (QPSK) spread-spectrum communication system. The efficiency of the system is analyzed by computing the bit error rate under different signal to noise ratio conditions. These results are compared with systems that employ Golden code and other typical pseudorandom sequences.

Keywords: pseudorandom sequences, cellular automata, spread spectrum.

 

Resumen

Métodos de sistemas dinámicos se han estado utilizando recientemente en sistemas digitales de comunicación de espectro expandido. La expansión del espectro mediante el uso de una secuencia pseudo-aleatoria de frecuencia mayor que la frecuencia de la señal de información es la clave que lo caracteriza para su robustez en contra de la interferencia de la señal en el canal. En este trabajo se propone generar secuencias pseudo-aleatorias mediante el uso de autómatas celulares y verificar que esta secuencias tengan las propiedades necesarias que se requieren para sistemas de comunicación modernos. Las secuencias generadas con autómatas celulares son probadas en un sistema de espectro expandido que utiliza modulación por cuadratura de fase QPSK. La eficiencia del sistema es analizada mediante el cálculo de la taza de error de bit bajo diferentes condiciones de la razón señal a ruido. Estos resultados son comparados con sistemas que emplean otras secuencias pseudo-aleatorias y secuencias Golden code.

 

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