| Solving accurate localization system problems is one of the main research directions in the field of Wireless Capsule Endoscopic(WCE).The Radio Frequency(RF)positioning method has a pivotal position in the localization field,and these methods of it are very suitable for solving positioning problem for complicated human environment.The field of RF propagation modeling is extremely diverse and has many facets,both technical and philosophical.The models presented herein arethose that I perceive as the accepted.They are may be the best choice for a particular application.In order to accurately estimate(build)the radio signal propagation attenuation model,especially inside the gastro-intestine(GI)tract of the human body,the RF absorption characterization in human body is investigated.This characterization provides a criterion to design the Received Signal Strength(RSS)based localization system for the objective inside the human body.The paper presents an algorithm for localization of endoscopic capsules inside the human body.The goal is to determine the position of capsules by measuring the power of received electromagnetic signal on the human skin taking into account losses within the body.Simulation results prove its high accuracy and indicate the optimal antenna configuration.Then analytical formulas are derived for the Cramér–Rao lower bound(CRLB)for capsule positioning when distance and azimuth angle measurements are employed to estimate the location of the capsule.The CRLB analysis can be employed to quantify the best achievable location estimation performance.We also present some numerical results to show the CRLB for three scenarios.The results show that in the most realistic scenario,when the shadowing is spatially correlated and distance dependent and the standard deviation of noise is 10 dB,the maximum square root of CRLB is 3.8 mm.Overall,the result of this paper suggests that it is possible to use received signal strength such as measured for location estimation of a WCE. |
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