Wireless Sensor Networks

The INERTIA team researches the fundamental issues associated Body Sensor Networks (BSNs) including the tradeoffs associated with wearability, system capabilities, power consumption, dynamics environment adjustment, etc.  Currently, a BSN system architecture is being designed that allows for dynamic calibration of data processing and transmission/storage to adjust for variable incoming data rates and dynamic wireless channel characteristics. The architecture shown below illustrates the use of both a data controller and a destination controller for runtime optimization of tradeoffs between power consumption, computational complexity, and signal fidelity. This system architecture is intended for implementation on resource constrained platforms common to BSN nodes.

In addition, the INERTIA team is involved in research exploring alternatives to RF communications in body area networks (BANs).  One promising alternative is Body-Coupled communication. This physical link medium uses the human body as a communication channel, thus requiring all transmitting and receiving nodes to directly contact the skin. Unlike existing BSNs, the effects due to external interference and body-induced attenuation are reduced considerably. Furthermore, coupling the energy into the body instead of the air increases both transmission energy efficiency and privacy.  It’s important to understand and design for the physical means of communication across the body. In principal, there are three approaches to this problem shown below.

First, a circuit can be implemented that passes current through the body directly, with the resulting signal captured at an output node. In this implementation, the input transmitter and receiver nodes must share a common reference connected by a wire, which is not desirable for wearability. Second, electrostatic coupling allows for current transfer through the body, but the common reference that the transmitter and receiver nodes share is “earth ground” to which they are both capacitively coupled. Originally explored by T.G. Zimmerman, this means of communication can be sensitive to its operating environment, an undesirable characteristic when designing robust and reliable systems.

The third method treats the body transmission channel as a waveguide, allowing for electromagnetic signaling between contacts of a transmitter and receiver. With the selection of an appropriate carrier frequency and modulation scheme, high data-rate communication can exist between two nodes coupled to the body with no external connections and virtually no dependence on the external environment. It is generally assumed that lower frequencies are most easily passed through the body due to the body’s absorption characteristics, so a low frequency carrier is preferred.  Body-coupled communication offers transmission power advantages over microwave communication by reducing the amount of wasted radiated power beyond the body-area. This principle also creates opportunities for higher spatial reuse in and between BSNs and for better assurance of privacy since there will be little to no interference from neighboring systems.