Medium Access Control and Rate Adaptation for Ultrasonic Intrabody Sensor Networks

The use of wirelessly internetworked miniaturizedbiomedical devices is promising a significant leap forward inmedical treatment of many pervasive diseases. Recognizing thelimitations of traditional radio-frequency wireless communicationsin interconnecting devices within the human body, in thispaper, we propose for the first time to develop network protocolsfor implantable devices based on ultrasonic transmissions. Westart off by assessing the theoretical feasibility of using ultrasonicwaves in human tissues and by deriving an accurate channelmodelfor ultrasonic intrabody communications. Then, we propose a newultrasonic transmission and multiple access technique, which werefer to as Ultrasonic WideBand (UsWB). UsWB is based on theidea of transmitting information bits spread over very short pulsesfollowing a time-hopping pattern. The short impulse durationresults in limited reflection and scattering effects, and the lowduty cycle reduces the impact of thermal and mechanical effects,which may be detrimental for human health. We then developa multiple access technique with distributed control to enableefficient simultaneous access by mutually interfering devicesbased on minimal and localized information exchange and onmeasurements at the receiver only. Finally, we demonstrate theperformance of UsWB through a multiscale simulator that modelsthe proposed communication system at the acoustic wave level, atthe physical (bit) level, and at the network (packet) level. We alsovalidate the simulation results by comparing them to experimentalresults obtained with a software-defined testbed.