Accuracy of RSS-Based RF Localization in Multi-capsule Endoscopy

In this paper, we derive and analyze cooperative localization bounds for endoscopic wireless capsule as it passes through the human gastrointestinal (GI) tract. We derive the Cramer-Rao bound (CRB) variance limits on location estimators which use measured received signal strength (RSS). Using a three-dimension human body model from a full wave simulation software and log-normal models for RSS propagation from implant organs to body surface, we calculate bounds on location estimators in three digestive organs: stomach, small intestine and large intestine. We provide analysis of the factors affecting localization accuracy, including various organ environments, external sensor array topology, number of pills in cooperation and the random variations in transmit power of sensor nodes. We also do localization accuracy analysis for the case when transmit power of the sensor is random with known priori distribution. The simulation results show that the number of receiver sensors on body surface has more influence on the accuracy of localization than the number of pills in cooperation inside the GI tract, The large intestine is affected the most with the transmit power randomness.