Wireless control systems can sense, control and act 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, wavelet coding is a good alternative for wireless communications for its robustness to the effects of multipath and 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 evaluates 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 performance gains obtained by 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 loop.
There are control systems in which sensors, actuators and controllers can't communicate by wired networks. In these environments, the use of wireless communications system is an alternative, but this can create other problems in the system, like delay and information loss. This paper investigates the performance of technique a Model Based Control (MBC) used to improve the response of a nonlinear invariant system, using a analogic circuit to simulate a tank level control, and analyzing the control behavior considering a communication with information loss. The results demonstrated that the technique improves the wireless control system.
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