The evolution of wireless technology has brought to reality wireless personal area networks and body area networks (PANs and BANs). Many challenges exist in building these wireless sensor systems including sensor size, DC power techniques, wireless signal interference and coupling from static and dynamic objects including people, etc. Also, much work is still needed in determining the target applications and in the practical development of these systems. The potential use of these systems in various medical applications makes it critical to understand their performance (e.g. bit error rate, positioning accuracy) in medical environments.