Adaptive Wavelet Coding Applied in a Wireless Control System

Abstract

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.

Design of Wavelet-Encoded Symbol Constellations for Cyclostationary Spectrum Sensing

“…Simplicity regarding the wavelet coding process led to the investigation of this transmission technique applied to di erent communication scenarios, such as at fading channels [6], frequency selective channels [4], analysis of channel estimation errors [7,8], and identi cation of modulation schemes designed by genetic algorithms [9], in OFDM systems on a 4.9 Gbps W-Band Radio-over-Fiber Link [10] and in wireless adaptive control systems [11].…”

“…In [10], a 2 × 128-size matrix was used to enable communications on an 80 GHz carrier frequency real fiber radio system. In [11], a small (2 × 8) matrix was used to enable a microcontrolled wireless loop control system. However, the wavelet coding technique has not yet been investigated in scenarios where systems employ spectrum sensing and dynamic spectrum access.…”