Subsampling OFDM-Based Ultrasonic Data Communication Through Metallic Channels for Monitoring of Cargo Containers

An enhanced ultrasonic communication system based on piezoelectric transducers for monitoring of goods in cargo containers is presented. The proposed system consists of several sensors placed inside the container whose data are collected and transmitted outside of it. Data transmission is carried out by an ultrasonic communication channel in order to avoid drilling the wall of the container. The proposed data communication system is based on the transmission of a 128-OFDM signal. This modulation has been chosen due to its robustness to channels with frequency-selective fading and its spectrum efficiency. In order to increase the signal bandwidth and to reduce the power consumption at the internal node (transmitter), the proposed system exploits the non-linearity of the metallic channel to transmit at higher resonance frequencies. Moreover, power consumption at the external node (receiver) is reduced by using a subsampling-based receiver, which allows its implementation through low-cost electronics.