Echo-Cancellation for Ultrasonic Data Transmission through a Metal Channel

The process control industry has shown great interest in implementation of low cost, low power wireless sensor networks. Such networks are much easier to deploy and reconfigure compared to wired alternatives. In this paper, we describe the use of radio-frequency (RF) based sensor networks in sensing and control applications on naval vessels. In this environment, metal bulkheads (which divide the ship into watertight compartments) and other metallic obstacles can lead to unreliable network connectivity. We propose to address the challenge by augmenting the RF network with ultrasonic data repeaters. The repeaters are designed to pass data from one side of a watertight bulkhead to the other without requiring the bulkhead to be physically penetrated. Through experimentation, we observed that echoes of pulses transmitted through the ultrasonic channel (i.e. the bulkhead) lead to considerable intersymbol interference and hinder high data rate transmission. In this paper, we investigate the nature of this interference and propose a method of mitigating its effect. The method applies a pre-distortion filter to the data which leads to destructive interference that reduces the echo amplitude.