# Low-Power, High Data-Rate Digital Capsule Endoscopy Using Human Body Communication
## 1 Introduction  
Recently, information technology (IT) developments in the medical area have been in the spotlight in the new field of biomedical engineering. Wireless capsule endoscopy (WCE) is a good example. It has been considered to be an innovative technology for the diagnosis of issues in the human digestive system (e.g., in the esophagus, stomach, small intestine, large intestine, and colon) because it is possible to avoid the disadvantages of the inspection techniques used currently for digestive organs. These disadvantages include side-effects caused by taking sleep-inducers or analgesics, and the possibility of medical accidents, such as organ perforation due to incorrect insertion of the endoscope. In addition, there is the inconvenience and fear of patients related to inserting the endoscope (a long tube) into the body. In contrast, it is possible to observe the digestive tract comfortably and without the inconvenience and risk described above when people use WCE [1; 2; 3]. Effective WCE was first introduced by Given Imaging Inc. (Yogneam, Israel) in 2000. The PillCam SB made by Given Imaging was approved by the food and drug administration (FDA) in 2003. It has been used as an actual medical diagnostic apparatus since then. More recently, several other kinds of WCEs have been developed and manufactured to look into the small intestine; for example, the EndoCapsule produced by Olympus Inc. (Tokyo, Japan, 2005) and the MiRoCam made by Intromedic Co. (Seoul, South Korea, 2006) [1; 4]. A variety of studies have been conducted regarding WCE. One study area focuses on active capsule endoscopy, in which the posture or the motion of capsule is controlled to make observations not only in the small intestine, but also in other internal organs (the stomach and large intestine) with interior spaces that are larger than the capsules. Because the endoscope capsule is moved involuntarily through open spaces, it is difficult to obtain accurate images. Therefore, studies were conducted on active capsule endoscopy technologies to provide stable posture and movement in the various spaces to be examined [1; 5; 6; 7; 8]. Some other studies on image encoders employing image compression techniques to overcome the problem of a transceiver with limited data transfer capability have been progressed in capsule endoscopes image [1; 9; 10]. However, since there is a limit to the image compression method, in order to transmit the high resolution image, the transmitter supporting the high data rate is needed. Another area of WCE study has been the exploration of several communication standards: radio frequency (RF), ultra-wide band (UWB), and human body communication (HBC). The RF systems have a disadvantage in that a significant amount of the transmitted signal is absorbed and attenuated by the human body. Therefore, the use of a high-gain antenna is required to receive the weak signals [2; 3; 11; 12; 13]. Especially, the capsule endoscope is a device that uses the human body as a signal transmission channel, rather than a general RF air channel. Since the human body is made up of various materials with different conductivities and permittivities, such as skin, muscle, fat, bone, and various organs, the speed and direction of the transmission signal varies depending on the position of the capsule [14; 15]. Thus, signals transmitted outside the human body do not have isotropic characteristics. In this channel environment, complex 2D/3D array receiving antennas are used to receive signals anywhere outside the body [16; 17; 18]. Therefore, a technique that can select a channel more optimally while reducing the complexity is required. On the other hand, HBC is a new communication approach for transferring baseband data using the human body as the channel medium without the need for a cable channel or RF communication channel. HBC systems have an advantage in that they can be implemented using only digital logic without complex RF blocks.