Distributed MAC and Rate Adaptation for Ultrasonically Networked Implantable Sensors

The use of miniaturized biomedical devices implantedin the human body and wirelessly internetworked ispromising a significant leap forward in medical treatment ofmany pervasive diseases. Recognizing the well-understood limitationsof traditional radio-frequency wireless communicationsin interconnecting devices within the human body, in this paperwe propose for the first time to develop network protocols forimplantable devices based on ultrasonic transmissions. We startoff by assessing the feasibility of using ultrasonic propagation inhuman body tissues and by deriving an accurate channel modelfor ultrasonic intra-body communications. Then, we propose anew ultrasonic transmission and multiple access technique, whichwe refer to as Ultrasonic WideBand (UsWB). UsWB is basedon the idea of transmitting information bits spread over veryshort pulses following a time-hopping pattern. The short impulseduration results in limited reflection and scattering effects, and itslow duty cycle reduces the thermal and mechanical effects, whichare detrimental for human health. We then develop a multipleaccess technique with distributed control to enable efficientsimultaneous access by interfering devices based on minimaland localized information exchange and on measurements atthe receiver only. Finally, we demonstrate the performance ofUsWB through a multi-scale simulator that models the proposedcommunication system at the acoustic wave level, at the physical(bit) level, and at the network (packet) level.