Application of wavelet coding in a control system using wireless sensor networks

The advance in wireless sensor networking technology is increasing the number of control systems that use these networks to transmit the relevant variable to be measured and controlled, despite of the more intense distortions caused by wireless channels. The performance of wireless communications systems is mainly limited by fading produced by multipath propagation. In order to minimize the fading effects, channel coding and diversity techniques are often used in wireless systems. Among the known coding techniques in the literature, the wavelet coding presents an interesting alternative to overcome the multipath fading, since it gets performance gain by transmitting in time diversity without compromising spectral efficiency. This paper investigates the use of wavelet coding in a system that operates over a wireless channel to control the rotation frequency of the direct current motor. Aspects such as packet error probability performance, hardware complexity and processing delays due to wavelet coding are analyzed, as well as its beneficial effects on the control system. In the proposed system, the wavelet coding was embedded in PIC microcontroller and a radio transceiver XBee is used to establish a wireless link. The obtained results demonstrate a reduction of fading effects on the control signal, as well as, a low cost for hardware implementation and a small impact on system processing time.