Ultra-wideband pulse-based data communications for medical implants

Impulse radio (IR) ultra wideband (UWB) technology is assessed herein for wireless data communications with a capsule endoscope operating inside the digestive tract. The UWB channel is characterised for the frequency range of 1-5 GHz and line-of-sight (LOS) scenarios. Owing to the lack of a standardised mathematical model for in-body UWB signals, the channel characterisation is attained by using numerical simulations. Because of the lossy material properties of the human tissues, short delay spread of the in-body channel is observed. The design of a packet based IR-UWB transmitter is presented herein, considering the restrictions on power consumption, size, cost and complexity. A novel coherent receiver using a single-branch correlation scheme is proposed. The receiver system performance is optimised by adjusting the shape and the delay of the template pulse for providing maximum output of the correlator. Its bit-error-rate (BER) performance using bi-phase pulse amplitude modulation (BPAM) is evaluated. The effects of different templates on the system performance are also investigated. Fast synchronisation is achieved by using a bank of correlators; the number of correlator branches and the preamble length for successful synchronisation are estimated. This investigation reveals the feasibility of using IR-UWB for capsule endoscope fast data transmission.