For time-of-arrival-(TOA)-based indoor human tracking system, the wireless channel between human body surface and external reference node can be regarded as the source of inaccuracy. Since only the arrival time of direct path provides accurate range estimate, the nonline of sight caused by human body leads to undetectable direct path condition and thus results in a significant distance measurement error. In this paper, we measured TOA ranging error for indoor human tracking applications inside a typical office environment. A large number of TOA ranging samples was obtained and statistically analyzed. The TOA ranging error was modeled as a Gaussian random variable with the parameters, including position of target sensor, angle between human facing direction, and direction of transmitter–receiver, signal-to-noise ratio, and bandwidth of the system. As a validation of proposed model, excellent agreement has been found between empirical measurement and model-based software simulation.

Toward Accurate Human Tracking: Modeling Time-of-Arrival for Wireless Wearable Sensors in Multipath Environment

One of promising transmission technologies in wireless body area networks (BANs) is ultra-wideband (UWB) communication, which can provide high data rate for real-time transmission, and extremely low power consumption for increasing device longevity. However, UWB signals suffer from large attenuation in a wireless communication link, especially in implant BANs. Although several investigations on channel characterization have been far thus conducted for evaluating the UWB transmission performance, they have been limited to either computer simulations or experiments with biological-equivalent phantoms. Experimental evaluation with a living body has rarely been conducted, i.e., the performance in real implant BANs has been scarcely discussed. In this paper, therefore, we focus on a living animal experimental evaluation on the UWB transmission performance. To begin with, we develop an ultra-wideband impulse radio (UWB-IR) communication system with a multipulse pulse position modulation scheme, and then analyze the fundamental characteristics of the developed UWB-IR communication system by a liquid phantom experiment. Finally, we evaluate the performance of the developed UWB-IR communication system via the living animal experiment. From the experimental results, although we have observed that the path loss is more than 80 dB, the developed system can achieve a bit error rate of 10-2 within the communication distance of 120 mm with ensuring a high data rate of 1 Mb/s. This result first time gives a quantitative communication performance evaluation for the implant UWB transmission in a living body.

Experimental Evaluation of Implant UWB-IR Transmission With Living Animal for Body Area Networks

Ultrawideband (UWB) short-range communication systems have proved to be valuable in medical technology, particularly for implanted devices, due to their low-power consumption, low cost, small size, and high data rates. Neural activity monitoring in the brain requires high data rate (800 kb/s per neural sensor), and we target a system supporting a large number of sensors, in particular, aggregate transmission above 430 Mb/s (~512 sensors). Knowledge of channel behavior is required to determine the maximum allowable power to 1) respect ANSI guidelines for avoiding tissue damage, and 2) respect FCC guidelines on unlicensed transmissions. We utilize a realistic model of the biological channel to inform the design of antennas for the implanted transmitter and the external receiver under these requirements. Antennas placement is examined under two scenarios having contrasting power constraints. Performance of the system within the biological tissues is examined via simulation and experiment. Our miniaturized antennas, 12 mm x 12 mm, need worst-case receiver sensitivities of -38 and -30.5 dBm for the first and second scenarios, respectively. These sensitivities allow us to successfully detect signals transmitted through tissues in the 3.1-10.6-GHz UWB band.

Biological channel modeling and implantable UWB antenna design for neural recording systems.

Ultrawideband (UWB) radio technology for wireless implants has gained significant attention. UWB enables the fabrication of faster and smaller transceivers with ultralow power consumption, which may be integrated into more sophisticated implantable biomedical sensors and actuators. Nevertheless, the large path loss suffered by UWB signals propagating through inhomogeneous layers of biological tissues is a major hindering factor. For the optimal design of implantable transceivers, the accurate characterization of the UWB radio propagation in living biological tissues is indispensable. Channel measurements in phantoms and numerical simulations with digital anatomical models provide good initial insight into the expected path loss in complex propagation media like the human body, but they often fail to capture the effects of blood circulation, respiration, and temperature gradients of a living subject. Therefore, we performed UWB channel measurements within 1–6 GHz on two living porcine subjects because of the anatomical resemblance with an average human torso. We present for the first time, a path loss model derived from these in vivo measurements, which includes the frequency-dependent attenuation. The use of multiple on-body receiving antennas to combat the high propagation losses in implant radio channels was also investigated.

In-Body to On-Body Ultrawideband Propagation Model Derived From Measurements in Living Animals

Health care is getting a lot of attention. Especially
due to population aging, health care has to be made affordable in the future. There is a need for enabling in-body communication and also localization of sensors which are moving through the human body. The propagation of radio frequency signals through different layers of human tissue is analyzed. In contrast to other research the complex characteristics of human tissue are included
for both received signal strength and time of arrival methods. A multilayer model is developed to investigate the influences of different tissue layers on the absolute signal attenuation and travel time for signal propagation from in-body to on-body for in-body communication allocated frequencies: 403.5 MHz, 916.5 MHz, and 2.45 GHz. The analysis results show that the attenuation and delay in small intestine and muscle tissues have more influence on the total values than in fat tissue.

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Analysis of Radio Propagation Inside the HumanBody for in-Body Localization Purposes

A body area network is a radio communication protocol for short-range, low-power, and highly reliable wireless communication for use on the surface, inside, or in the peripheral proximity of the human body Combined with various biomedical sensors, BANs enable realtime collection and monitoring of physiological signals Therefore, it is regarded as an important technology for the treatment and prevention of chronic diseases, and health monitoring of the elderly The IEEE 802 LAN/MAN Standards Committee approved Task Group TG156 in December 2007 As a result of more than four years of effort, in February 2012, TG156 published the first international standard for BANs, IEEE Std 802156 Throughout the development of this standard, ample collaboration between the standardization group and the research community was required In particular, understanding the radio propagation mechanisms for BANs demanded the most research effort Technical challenges were magnified for the case of implant communication because of the impossibility of conducting in-body measurements with human subjects Therefore, research in this field had to make use of intricate computer simulations This article outlines some of the research that has been done to obtain accurate propagation models supporting the standardization of implant communication in BANs Current research to enhance the channel models of IEEE Std 802156 through the use of ultra wideband signals for implantable devices along with physical measurements in animals is also presented

K. Sayrafian-Pour

Papers

Propagation models for IEEE 802.15.6 standardization of implant communication in body area networks