Desenvolvimento de uma codificação wavelet adaptativa para um sistema de controle sobre canais sem fio

Abstract

Wireless control systems have the capacity of sensing, control and actuation on the information exchanged between the wireless sensor nodes in a control loop. However, the exchanged information becomes susceptible to the degenerative effects produced by the multipath propagation. In order to minimize the destructive effects characteristic of wireless channels, several techniques have been investigated recently. Among them, the wavelet coding is a good alternative for the wireless communications by their robustness to the effects of the multipath and by its low computational complexity. This work proposes an adaptive wavelet coding whose parameters of code rate and signal constellation can vary according to the fading level, and evaluate the use of this transmission system in a control loop implemented by wireless sensor nodes. The performance of the adaptive system was evaluated in terms of bit error rate (BER) versus Eb=N0 and spectral efficiency, considering a time-varying channel with flat Rayleigh fading, and in terms of processing overhead on a control system with wireless communication. The results obtained through computational simulations and experimental tests show the efficiency of the insertion of the adaptive wavelet coding in a control loop with nodes interconnected by wireless link. These results enable the use of this technique in a wireless link control mesh, bringing it one step even closer to being applied in a practical control system.