Variation-Aware System Design Simulation Methodology for Capacitive BCC Transceivers
Abstract: Capacitive body coupled communication (BCC), frequency range 500 kHz to 15 MHz, is considered an emerging alternate short range wireless technology which can meet the stringent low power consumption (< 1 mW) and low data rate (< 100 kbps) requirements for the next generation of connected devices for applications like internet-of-things (IoT) and wireless sensor network (WSN). But a reliable solution for this mode of communication covering all possible body positions and maximum communication distances around the human body could not be presented so far, despite its inception around 20 years back in 1995. The uncertainties/errors associated with experimental measurement setup create ambiguity about the measured propagation loss or transmission errors. The reason is the usage of either earth grounded lab instruments or the direct coupling of earth ground with transmitter/receiver or the analog front end cut-off frequency limitations in a few MHz region or the balun to provide isolation or the measurements on simplified homogeneous biological phantoms. Another source of ambiguity in the experimental measurements is attributed to the natural variations in human tissue electrophysiological properties from person to person which are also affected by physical factors like age, gender, number of cells at different body locations and humidity. The analytical models presented in the literature are also oversimplified which do not predict the true propagation loss for capacitive BCC channel.An attempt is being made to understand and demonstrate, qualitatively and quantitatively, the physical phenomenon of signal transmission and propagation characteristics e.g., path loss in complex scenarios for capacitive BCC channel by both the experimental observations/measurements and simulation models in this PhD dissertation. An alternate system design simulation methodology has been proposed which estimates the realistic path loss even for longer communication distances > 50 cm for capacitive BCC channel. The proposed simulation methodology allows to vary human tissue dielectric/thickness properties and easily integrates with the circuit simulators as the output is in the form of S-parameters. The advantage is that the capacitive BCC channel characteristics e.g., signal attenuation as a function of different physical factors could be readily simulated at the circuit level to choose appropriate circuit topology and define suitable system specifications. This simulation methodology is based on full-wave electromagnetic analysis and 3D modeling of human body and environment using their conductivity, permittivity, and tangent loss profile to estimate the realistic propagation loss or path loss due to their combined interaction with the electrode coupler for capacitive BCC channel. This methodology estimates the complex path impedance from transmitter to receiver which is important to determine the matching requirements for maximum power transfer. The simulation methodology also contributes towards better understanding of signal propagation through physical channel under the influence of different electrode coupler configurations. The simulation methodology allows to define error bounds for variations in propagation loss due to both numeric uncertainties (boundary conditions, mesh cells) and human body variation uncertainties (dielectric properties, dielectric thicknesses) for varying communication distances and coupler configuration/sizes.Besides proposing the simulation methodology, the digital baseband and passband communication architectures using discrete electronics components have been experimentally demonstrated in the context of IoT application through capacitive BCC channel for data rates between 1 kbps to 100 kbps under isolated earth ground conditions. The experimental results/observations are supported by the simulation results for different scenarios of capacitive BCC channel.The experimental and simulation results help in defining suitable system specifications for monolithic integrated circuit design of analog front end (AFE) blocks for capacitive BCC transmitter/receiver in deep submicron CMOS technologies.
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