In this paper, we analyze the current issues for designing a communications system among implant and on-body nodes employing ultra wideband (UWB) technology. As a result, we propose a modulation scheme ad-hoc for this environment that besides being suitable for this propagation channel, it allows to employ antenna diversity on the on-body nodes. Antenna diversity permits to improve signal to noise ratio and avoid using transmission diversity, which limits the exposition of human tissue to electromagnetic radiation. © 2011 IEEE.