A wireless capsule endoscope (WCE) is a promising medical device for diagnosis of digestive organs, which takes pictures inside digestive organs, such as large and small intestines and transmits them through implant wireless communications. In a realistic WCE scenario, it is important to precisely estimate the WCE location. Generally, the superiority of TOA-based localization over RSSI-based localization has been pointed out in many papers in wireless communication systems. However, because the propagation speed inside of a human body varies due to the influence of its biological tissues (namely, the relative permittivity of human tissues), the realization of precise TOA-based localization needs to accurately estimate the propagation velocity of implant communication signals.

So, in this paper, we propose a TOA-based method for joint location/relative permittivity estimation, and then compare the performances between TOA- and RSSI-based WCE location estimation methods. Our computer simulation results reveal that, the TOA-based localization with accurate relative permittivity information outperforms the RSSI-based localization in terms of the localization accuracy, whereas the RSSI-based localization is advantageous if accurate relative permittivity is not obtained. Additionally, the proposed TOA-based localization can achieve not only better localization accuracy than that of the RSSI-based localization but also accurate averaged relative permittivity estimation.