Analog front-end for human body communications and feasibility study for medical services

Abstract

Human body communications (HBC), where the human body is used as a transmission medium, is a promising candidate for a ubiquitous network and has been standardized by the IEEE 802.15.6 as one of the physical layer for body area networks (BAN). An improved analog front-end with a sensitivity of -95.6 dBm for HBC was presented whereby a spread signal with a group of 64 Walsh code is directly transferred through a human body at a data rate of 2 Mbps. A prototype capsule endoscope has been implemented to evaluate a feasibility on the adoption of HBC for medical services while electrical specifications of as a medical device using HBC was derived from the basic restrictions of international standard and regulations. Accurate channel model is an essential prerequisite for developing the reliable and efficient transmission method. A human body channel model was investigated in terms of signal transmission through the human body and interference induced on the human body from outside sources. Frequency response that corresponds to fingertips of the one hand to the other and the deviation of 10 dB were presented in the range of 0 - 55 MHz with steps of 5 MHz using measurement-based time domain method. Furthermore, reflection of the isolation between the transmitter and the receiver increased the average magnitude of signal loss. Statistical characteristics of interference induced on the human body due to the radiated electromagnetic fields (EMF) from the outside sources was defined as noise with a Gaussian distribution that has the zero mean and variance values of $2.55 \times 10^{-5}$ respectively. Based on comprehensive understanding on channel environment including propagation loss as well as interference, a novel transmission technique named frequency selective digital transmission (FSDT) in which a group of spread code is directly transmitted through the human body was proposed. From the study on interference, there is the frequency band between 10 MHz and 20 MH...