Software-Defined Ultrasonic Communication System With OFDM for Secure Video Monitoring

Ultrasonic communication is a desirable method for information transfer through solid channels such as metallic bars, plates, or pipes by overcoming the physical barriers that prevent conventional wired or radiofrequency transmission. In this paper, we investigate the architecture of a reconfigurable software-defined ultrasonic communication (SDUC) platform that can make use of the complete channel bandwidth for real-time video transmission through a highly reverberant solid channel. Reverberations in solid channels are complex and generated by surface wave, lamb wave, longitudinal wave, shear wave, reflection, refraction, dispersion, mode conversion, and scattering phenomena. To explore the multipath and fading effects on bitrate, experimental studies were performed using an aluminum rectangular bar (ARB) of 25, 40, and 50 cm channel length. We investigated the feasibility of utilizing orthogonal frequency-division multiplexing (OFDM) combined with quadrature amplitude modulations (QAM) for peak bitrate performance. Design strategies and guidelines have been established for the best solutions to combat intersymbol interference caused by the severe reverberation inherent to ultrasonic solid channels. A practical solution for video transmission, adhering to the Digital Video Broadcasting Terrestrial (DVB-T) standard, is also examined for video streaming transmission of 240p, 480p, and 720p resolutions at 20 frames per second across an ARB channel. For experimental studies and performance evaluation, we designed a high-performance reconfigurable system-on-chip (SoC) SDUC platform for video transmission and bit error rate (BER) assessment. Through experimental studies for ultrasonic channel analysis, we achieved a peak video transmission rate of 1074 kbps with 3.3
$\times \,\,10 ^{-4}$
BER despite reverberation, the multipath effect, and signal fading within the ARB channel.