Enabling Ultrasound In-Body Communication: FIR Channel Models and QAM Experiments

Ultrasound waves pose a promising alternative to the commonly used electromagnetic waves for intra-body communication. This due to the lower ultrasound wave attenuation, the reduced health risks, and the reduced external interference. Current state-of-the-art ultrasound designs, however, are limited in their practical in-body deployment and reliability. This stems from their use of bulky, focused transducers, the use of simple modulation schemes or the absence of a realistic test environment and corresponding realistic channel models. Therefore, this paper proposes a new, ultrasound, static emulation test bed consisting of small, omnidirectional transducers, and custom gelatin phantoms with additional scattering materials. Using this test bed, we investigate different in-body communication scenarios. Multiple communication channels were extracted and mapped onto finite impulse response (FIR) channel models, which are verified and open sourced for future research. Furthermore, a basic quadrature-amplitude modulation (QAM) modem was built to assess the communication performance under various modulation schemes. A link was established using 4-QAM and 200 kbit/s resulting in a BER <1e-4 at received Eb/No of 13dB. Identical results were obtained by computer simulations on the FIR channels, which makes the extracted FIR channels suitable for the design of future ultrasound in-body communication schemes.