Raúl Chávez-Santiago

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

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 TG15.6 in December 2007. As a result of more than four years of effort, in February 2012, TG15.6 published the first international standard for BANs, IEEE Std 802.15.6. 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 802.15.6 through the use of ultra wideband signals for implantable devices along with physical measurements in animals is also presented.

Architecture of an ultra wideband wireless body area network for medical applications

The utilization of wireless technology in traditional medical services provides patients with enhanced mobility. This has a positive effect on the recovery speed of a patient after major surgical procedures or prolonged illness. This paper presents the architecture of a healthcare wireless network that exploits the capabilities of ultra wideband technology (UWB) for medical sensing and in-body tracking and imaging. The communication requirements for an UWB wireless body area network (WBAN) are enlisted. Both on-body and in-body sensors are taken into consideration. Special attention is paid to the requirements of a capsule endoscope, which is one of the most throughput-demanding sensors in modern telemedicine.

5G: The Convergence of Wireless Communications

As the rollout of 4G mobile communication networks takes place, representatives of industry and academia have started to look into the technological developments toward the next generation (5G). Several research projects involving key international mobile network operators, infrastructure manufacturers, and academic institutions, have been launched recently to set the technological foundations of 5G. However, the architecture of future 5G systems, their performance, and mobile services to be provided have not been clearly defined. In this paper, we put forth the vision for 5G as the convergence of evolved versions of current cellular networks with other complementary radio access technologies. Therefore, 5G may not be a single radio access interface but rather a “network of networks”. Evidently, the seamless integration of a variety of air interfaces, protocols, and frequency bands, requires paradigm shifts in the way networks cooperate and complement each other to deliver data rates of several Gigabits per second with end-to-end latency of a few milliseconds. We provide an overview of the key radio technologies that will play a key role in the realization of this vision for the next generation of mobile communication networks. We also introduce some of the research challenges that need to be addressed.

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

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.

Ultra-wideband pulse-based data communications for medical implants

Impulse radio (IR) ultra wideband (UWB) technology is assessed herein for wireless data communications with a capsule endoscope operating inside the digestive tract. The UWB channel is characterised for the frequency range of 1-5-GHz and line-of-sight (LOS) scenarios. Owing to the lack of a standardised mathematical model for in-body UWB signals, the channel characterisation is attained by using numerical simulations. Because of the lossy material properties of the human tissues, short delay spread of the in-body channel is observed. The design of a packet based IR-UWB transmitter is presented herein, considering the restrictions on power consumption, size, cost and complexity. A novel coherent receiver using a single-branch correlation scheme is proposed. The receiver system performance is optimised by adjusting the shape and the delay of the template pulse for providing maximum output of the correlator. Its bit-error-rate (BER) performance using bi-phase pulse amplitude modulation (BPAM) is evaluated. The effects of different templates on the system performance are also investigated. Fast synchronisation is achieved by using a bank of correlators; the number of correlator branches and the preamble length for successful synchronisation are estimated. This investigation reveals the feasibility of using IR-UWB for capsule endoscope fast data transmission.

On ultra wideband channel modeling for in-body communications

Innovative medical applications such as implant wireless sensors for health monitoring, automatic drug deliverance, etc. can be realized with the use of ultra wideband (UWB) radio technology. Nevertheless, for efficient design of wireless systems operating inside the human body a radio communication channel model is essential. Although a lot of research effort has recently been devoted to the characterization of the on-body UWB radio communication channel, just a few works describing the radio propagation inside the human body have been reported. To address this problem, a computational study of the propagation of UWB signals through human tissues in the 0.1-1 GHz and 1-6 GHz frequency bands is presented in this paper. This is based on numerical simulations using a heterogeneous anatomical model of the human body with frequency dependent tissue material properties. Subsequently, a statistical channel model is introduced for UWB in-body communications in the 1-6 GHz frequency band. The model is provided for two typical depths inside the human chest. This work contributes to the practical design of UWB medical implant communication systems.

Antennas and circuits for ambient RF energy harvesting in wireless body area networks

In this paper, we identify the spectrum opportunities for radio frequency (RF) energy harvesting through power density measurements from 350 MHz to 3 GHz. The field trials have been performed in Covilhâ by using the NAKDA-SMR spectrum analyser with a measuring antenna. Based on the identification of the most promising opportunities, a dual-band band printed antenna operating at GSM bands (900/1800) is proposed, with gains of the order 1.8-2.06 dBi and efficiency 77.6-84%. Guidelines for the design of RF energy harvesting circuits and choice of textile materials for a wearable antenna are also discussed. Besides, we address the guidelines for designing circuits to harvest energy in a scenario where a wireless body area network (WBAN) is being sustained by a TX91501 Powercasf® RF dedicated transmitter and a five-stage Dickson voltage multiplier responsible for harvesting the RF energy. The IRIS motes, considered for our WBAN scenario, can perpetually operate if the RF received power attains at least -10 dBm.

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

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.

Ultrawideband technology in medicine: a survey

The utilization of wireless technology in traditional medical services provides patients with enhanced mobility. This has a positive effect on the recovery speed of a person after major surgical procedures or prolonged illness. Ultrawideband (UWB) radio signals have inherent characteristics that make them highly suitable for less invasive medical applications. This paper surveys our own and related recent research on UWB technology for medical sensing and communications. Some research perspectives in the aforementioned topics are suggested too.

An ultra wideband communication channel model for capsule endoscopy

Capsule endoscopy is an increasingly popular alternative to a tube-based endoscope used in diagnosing gastrointestinal diseases. It enables the inspection of areas that are not easily accessible using traditional endoscopy and reduces patient discomfort. In addition to transferring high-capacity demanding image data, the capsules wireless interface must provide a wireless link that enables real-time positioning and tracking of the capsule. Ultra wideband (UWB) interfaces have great potential for the communication links of this application due to their inherent low power consumption, high transmission rates, accurate localization properties and simple electronics. However, accurate knowledge of the propagation channel is essential for efficient design of such UWB wireless communication systems. This paper presents a channel model for the propagation of a UWB pulse in the digestive tract in the 3.4–4.8 GHz frequency band. For the development of this model, numerical electromagnetic (EM) simulations were conducted using a voxel anatomical model that includes the dielectric properties of human tissues; using this EM simulator the channel responses of many in-body probes were computed. Based on the analysis of the obtained data we provide the mathematical expressions to calculate the average path loss and its distribution at several receiver locations surrounding the abdomen. Our proposed model gives designers an important tool that approximates well the digestive tracts in-body channel properties, thereby eliminating the need for time consuming and complex numerical simulations.