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

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

Kaveh Pahlavan (Worcester Polytechnic Institute, USA), Yunxing Ye (Worcester Polytechnic Institute, USA), Ruijun Fu (Worcester Polytechnic Institute, USA) and Umair Khan (Worcester Polytechnic Institute, USA)
DOI: 10.4018/jertcs.2012070102


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.
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In the past decade miniaturization and cost reduction of semiconductor devices has allowed the design of small low cost computing and wireless communication devices used as sensors in a variety of popular wireless networking applications and this trend is expected to continue in the next few decades. It is expected that a myriad of new applications designed around sensor technologies will emerge to stimulate a huge industrial growth. One of the most promising areas of industrial growth associated with this industry is the body sensor networks that are also referred to as the body area networks (BAN) (Yang & Yacoub, 2006).

These networks are expected to connect wearable and implantable sensory nodes together and with the Internet to support numerous applications ranging from traditional externally mounted temperature meters or implanted pace makers up to emerging blood pressure sensors, eye pressure sensors for glaucoma and smart pills for health monitoring and precision drug delivery.

To support the growth of this industry, recently the Federal Communication Commission (FCC) has allocated specific bands for Medical Radio Communication Services (MedRadio) (FCC, 2008) and the IEEE 802.15.6 is formed to address the standardization aspects of these emerging technologies. The IEEE 802.15.6 models the characteristics of the radio propagation inside and around the human body and defines wireless networking technologies for wearable and implanted sensor networks (Aoyagi, 2006). The standards recommend that the transmission power should be around 25 μW to keep the EM emissions at a healthy level (FCC, 2008).

Certainly for all BAN applications power efficient modulation and medium access control methods are needed in principle and a number of researchers are working on that topic (Kim, 2008). The important and the fundamental issue presented in this paper is the localization of objects inside the human body to assist the discovery of methods for navigating emerging micro-robots in wireless medical applications such as capsule endoscopy. This is a new field of research that is gaining some momentum in the recent years (Aoyagi, 2009; NIST, 2011).

Understanding the nature of signal propagation is the key to the design of precise localization for any wireless network (Pahlavan, 2005). Therefore, the first step in research is to start a measurement and modeling program to understand the nature of signal transmission inside the human body. Today, the existing literature in measurement and modeling for understanding the propagation in and around the human body is fragmented and it does not pay attention to localization inside the human body (Aoyagi, 2009). The IEEE 802.5.6 is working on creating a comprehensive channel model for different scenarios and frequency bands used for communication applications (Hagedorn, 2008). There is a need for research in understanding the behavior of RF signal propagation inside the human body for localization applications.

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