Advanced Wireless Transmission for Skin Patches and Implants Smart Antenna Research Laboratory Mary Ann Ingram (mai@gatech.edu) and Aravind Kailas School of Electrical and Computer Engineering Preliminary Results Implanted Sensors Statement of the Problem Wireless transceivers on or in the body have a variety of applications in telehealth and telemedicine, and provide the user improved mobility and quality of life: Remote patient monitoring Neuro-stimulation and sensing Athletic training aides Remote drug delivery However, body tissues strongly attenuate radio waves, making wireless transmission inherently unreliable Radio connectivity becomes a function of body position and proximity to the wireless access point or hub device Tissue heating and other issues imply severe limits on radio transmitter power Battery replacement is at best inconvenient and at worst (for implants) creates a risk to the patient Skin Patch Sensors To wireless hub (PDA or bedside) Power gain of about 14 dBm per antenna (range of 4m) As distances between transmitters increases (i.e. as correlation decreases), power gain improves Reduction in fade margin is achieved Range extension Testbed for Cooperative Transmission Packet Delivery Ratio Software Defined Radio GNURadio is open source toolkit for building and deploying SDR systems 20 USRP board and 2.4GHz d’boards are used for testbed Our Solution: Cooperative Transmission Telemetry Network (TeNt) Control and monitor GNURadio network by utilizing Micaz motes One or more radios help other radios by transmitting copies of the signal The copies are combined in the physical layer of the receiver- leading to improved reception The benefits of CT: Range Extension in highly attenuating environments Reduces tissue heating by sharing the transmission energy across multiple locations Gain from multiple cooperating radios Average Distance = 5m N = Number of Relays 3 mm Electronic device (e.g. switch) Long wires “Pore” A Concept: Long-Wire Implant Bus (LIMBUS) 2nd conductor not used Electrode The PM/ICD, and neurostimulators can all operate via long wires, 40 cm and longer, lying in a vein and/or under the skin. ICD wires implanted in 18 year olds are expected to last 50 years or more. The LIMBUS long wire would be a generic integrated platform, supporting multiple sensors, electrodes, energy harvesters, a microprocessor and a radio. The wire therefore has a network bus architecture, with the various devices connecting to it through electronic switches. (a) (b) 100 10-1 10-2 10-3 10-4 10-5 10-6 Digital Sensor with no relays Electrode Digital Sensor Energy Harvester (c) (d) Advantages: Distributed sensing, stimulation, and computing on a single-wire platform that can be implanted using relatively simple and conventional surgical techniques. Prior art has a long wire for every electrode, and implantation for distributed electrodes is much more complicated Uses mature wire technology as a basis More efficient energy harvesting, because of multiple and distributed devices Potentially more efficient antenna because of its length (a) single device, (b) electrode detail (c) digital sensor detail, (d) long wire with integrated devices Disadvantages: Higher mechanical load on the wire More friction (because of small lumps) during surgical implantation More insertion loss (because of the switches) on the electrodes More electrical noise on the electrodes (from the digital electronics) ~19 dB power gain Prob. outage TX/RX Arms of the dipole The secondary conductor with two relays 0 5 10 15 20 25 SNR (dB) When it is not a bus, LIMBUS is an efficient dipole antenna Source: J. N. Laneman, Cooperation in Wireless Networks: Principles and Applications. Springer, 2006, ch. Cooperative Diversity: Models, Algorithms, and Architectures, pp. 163-188.