The rapid development of electronic technology and wireless communication enables many kinds of medical sensor devices, which are designed for monitoring the human body. This paper focuses on swallowable medical devices like wireless capsule endoscopes (WCEs) [1]. They are swallowed by patients and go through the gastrointestinal (GI) tract to collect the vital signs of the human body, and send them to a data receiver which is attached onto the abdomen of the human body [2,3]. It can be imagined that more than one medical device can be swallowed and they cooperate to finish some common task, like image segmentation capturing, long term and short term monitoring, etc. [4]. In these scenarios, the sensors and the data receiver form a kind of body sensor network (BSN) [5]. Figure 1 shows a simple architecture of this swallowable BSN. Several sensor devices are moving or staying in the GI tract. They collect the sensing data and send them to the coordinator in a single-hop or multi-hop way. The coordinator then transfers the data to a nearby or remote monitor for diagnosis by doctors.