Yunxing Ye

Performance bounds for RF positioning of endoscopy camera capsules

In this paper, we evaluate the factors affecting the accuracy achievable in localization of an endoscopic wireless capsule as it passes through the digestive system of the human body. Using a three-dimension full electromagnetic wave simulation model, we obtain bounds on the capsule-location estimation errors when the capsule is in each of three individual organs: stomach, small intestine and large intestine. The simulations assume two different external sensor arrays topologies. We compare these performance bounds and draw the conclusion that location-estimation errors are different for different organs and for various topologies of the external sensor arrays.

On the accuracy of RF positioning in multi-Capsule endoscopy

In this paper, we derive and analyze cooperative localization bounds for endoscopic wireless capsule as it passes through the human gastrointestin (GI) tract. We derive the Cramer-Rao lower bound (CRLB) 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 and number of pills in cooperation. 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.

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.

Challenges in Channel Measurement and Modeling for RF Localization Inside the Human Body

In this invited paper, the authors introduce an overview of the fundamentals of radio frequency RF channel measurement and modeling techniques needed for localization inside the human body. To address these fundamentals, the authors use capsule endoscopy as an example application. The authors first provide the results of the Cramer Rao Lower Bound CRLB for received signal strength RSS based endoscopy capsule localization, inside the human body, using existing path-loss models for radio propagation. Then challenges demanding further research are highlighted for attaining more precise localization using the time-of-arrival TOA based ranging techniques.

Doppler spread analysis of human motions for Body Area Network applications

Many current and future medical devices are wearable and the human body is used as a carrier for wireless communication, which implies that the human body is a crucial part of the transmission medium in Body Area Networks (BANs). In order to understand the propagation characteristics of the human body, it is imperative to analyze the Doppler spread spectrum, which is caused by human body motions. Using a network analyzer, Doppler spreads and coherence time of temporal variations caused by human body motions can be measured and analyzed using a single tone waveform for different scenarios in a shielded room. From the narrowband measurement results, the Doppler spread varies approximately from 0.6Hz to 12Hz for different scenarios, the RMS Doppler bandwidth is in the range from 0.6Hz to 4Hz, and the coherence time differs from 20ms to 1s, all of which are measured at the Medical Implant Communication Service (MICS) band, the Industrial Scientific Medical (ISM) band and the Ultra-Wideband (UWB) band. Root mean square fittings of three different functions to received signal strength measurements were performed for different scenarios. Results show that the Gaussian function generally provides a good fitting model, which is independent of center frequencies.

Bounds on performance of hybrid WiFi-UWB cooperative RF localization for robotic applications

Precise localization has attracted considerable traction in the area of cooperative assignments for robots in indoor applications. When dealing with indoor applications we are limited to the type of signals that can be used for precise localization which is our prime goal. There are limitations to the well known GPS and also vision-based modality where the non-line-of-sight (NLOS) conditions can significantly degrade the results. Hence there is a need for alternative approaches for more precise indoor localization. Precise localization information is an enabler for better coordinated tasks where multiple robots are at play. In this paper, the hybrid cooperative localization accuracy for a multi-robot operation is examined. We use a mix of empirical and theoretical models for ranging estimates in a typical indoor environment on the third floor of the Atwater Kent Laboratory (AKL) at Worcester Polytechnic Institute. The two widely used ranging techniques are Time Of Arrival (TOA) using Ultra-wideband (UWB) and Received Signal Strength (RSS) using WiFi signals. The Cramér-Rao-Lower-Bound (CRLB) on the performance of hybrid localization techniques are determined in our multi-robot operation scenarios based on empirical data for UWB TOA-based and the theoretical WiFi RSS-based ranging. The performance of the hybrid localization of robots are examined when the robots are equipped with UWB radios and operate in cooperative mode using known WiFi Anchors.

On effect of transmit power variance on localization accuracy in wireless capsule endoscopy

This paper presents an analysis on localization accuracy of a capsule used for wireless endoscopy application when there are random variations in transmit power of sensor nodes. We use a three-dimensional human body model and the log normal model for Received Signal Strength (RSS) radio propagation from the implant to the sensor nodes on the body surface to find accuracy bounds in three digestive organs, namely stomach, small intestine, and large intestine, which form the human Gastro-Intestinal (GI) track. The analysis is done using Bayesian Crameŕ-Rao bound assuming that the transmit power is random process with known prior distribution. We provide analysis of the factors affecting localization accuracy including various organ environment, external sensor array topology. The simulation results show that the capsule localization inside large intestine is affected the most with the transmit power randomness, while wireless capsule can be localized with best accuracy inside the small intestine. Finally, we propose an approach to improve the attainable accuracy bounds.

UWB characteristics of creeping wave for RF localization around the human body

There is much current interest in wireless networking of sensors deployed on and around the human body, in view of many potential applications for health monitoring. In this paper, we conducted ultra-wide-band (UWB) measurements around human body and a phantom in order to develop angle based channel models for body area network (BAN) and to compare the measurement results in these two environments. By analyzing certain channel parameters such as, time-of-arrival (TOA), distance-measurement-error (DME), received signal strength (RSS) and total path-loss, we discuss the influencing factors when the signal traveling around the human body. We also analyze the influence of the human body on TOA ranging accuracy.

Characteristic and Modeling of Human Body Motions for Body Area Network Applications

Many current and future medical devices are wearable and human body is used as a carrier for wireless communication, which implies human body to be a crucial part of the transmission medium in body area networks (BANs). In order to understand the propagation characteristics around human body, the statistical model is derived for communication links in the medical implant communication service band, industrial scientific medical band and ultra-wideband based on the narrowband measurement. The channel model of diffracting components around human body were different from one scenario to another. Moreover, second order statistics, including level crossing rate and fade duration, are presented for each scenario to evaluate the link quality and outage performance for on-body to on-body scenario. Using a network analyzer, Doppler spread spectrum in frequency domain and coherence time in time domain from temporal variations of human body movements are also analyzed from diverse perspectives. Additionally, the shape of Doppler spread spectrum is fitted to describe the relationship of power and frequency. The proposed on-body to on-body channel model for human body motions can be used to better design wireless network protocols for BANs.

RF localization inside human body: Enabling micro-robotic navigation for medical applications

In this paper we introduce issues relevant to understanding of the human body as a medium for radio frequency (RF) navigation of smart robots travelling inside the body for wireless medical applications. We provide the results of Cramer Rao Lower Bound (CRLB) for in-body localization using received signal strength (RSS) and we highlight challenges demanding further research for attaining more precise localization inside body using time-of-arrival (TOA) techniques.