On the Performance of In-Body RF Localization Techniques

Localization inside the human body using Radio Frequency (RF) transmission is gaining importance in a number of applications such as Wireless Capsule Endoscopy. The accuracy of RF localization depends on the technology adopted for this purpose. The two most common RF localization technologies use Received Signal Strength (RSS) and Time-Of-Arrival (TOA). This research first provides bounds for accuracy of localization of a Endoscopy capsule inside the human body as it moves through the gastro-Intestinal track with and without randomness in transmit power using RSS based localization with a triangulation algorithm. It is observed that in spite of presence of a large number of anchor nodes; the localization error is still in range of few cm, which is quite high; hence we resort to TOA based localization. Due to lack of a widely accepted model for TOA based localization inside human body we use a computational technique for simulation inside and around the human body, named Finite Difference Time Domain (FDTD). We first show that our proprietary FDTD simulation software shows acceptable results when compared with real empirical measurements using a vector network analyzer. We then show that, the FDTD method, which has been used extensively in all kinds of electromagnetic modeling due to its versatility and simplicity, suffers seriously because of its demanding requirement on memory storage and computation time, which is due to its inherently recursive nature and the need for absorbing boundary conditions. In this research we suggest a novel computationally efficient technique for simulation using FDTD by considering FDTD as a Linear Time Invariant (LTI) system. Then we use the software to simulate the TOA of the narrowband and wideband signals propagated inside the human body for RF localization to compare the accuracies of the two using this method

Accuracy of localization system inside human body using a fast FDTD simulation technique

Abstract-In this paper we analyze the accuracy of narrowband and wideband localization techniques inside the homogeneous human tissues using a fast finite difference time domain (FDTD) technique. In the narrowband localization, the phase of the received carrier signal is used for ranging measurements, whereas for the wideband transmission, the time of arrival (TOA) of the received signal is used. For fast computations, we introduce a new perspective to FDTD simulations of radio propagation by considering each simulation set for a given location of antennas as a Linear Time Invariant (LTI) discrete-time system. This way a set of simulations for a variety of transmitted waveforms can be reduced to only one simulation to determine the impulse response of the simulated channel between the two antennas and the convolution of the set of waveforms with this impulse response. A typical simulation using FDTD takes several minutes to a few hours and each convolution takes only a few seconds, resulting in a huge reduction in computational time