Implementing and Evaluating a Wireless Body Sensor System for Automated Physiological Data Acquisition at Home

Advances in embedded devices and wireless sensor networks have resulted in new and inexpensive health care solutions. This paper describes the implementation and the evaluation of a wireless body sensor system that monitors human physiological data at home. Specifically, a waist-mounted triaxial accelerometer unit is used to record human movements. Sampled data are transmitted using an IEEE 802.15.4 wireless transceiver to a data logger unit. The wearable sensor unit is light, small, and consumes low energy, which allows for inexpensive and unobtrusive monitoring during normal daily activities at home. The acceleration measurement tests show that it is possible to classify different human motion through the acceleration reading. The 802.15.4 wireless signal quality is also tested in typical home scenarios. Measurement results show that even with interference from nearby IEEE 802.11 signals and microwave ovens, the data delivery performance is satisfactory and can be improved by selecting an appropriate channel. Moreover, we found that the wireless signal can be attenuated by housing materials, home appliances, and even plants. Therefore, the deployment of wireless body sensor systems at home needs to take all these factors into consideration.Comment: 15 page

Models for the modern power grid

This article reviews different kinds of models for the electric power grid that can be used to understand the modern power system, the smart grid. From the physical network to abstract energy markets, we identify in the literature different aspects that co-determine the spatio-temporal multilayer dynamics of power system. We start our review by showing how the generation, transmission and distribution characteristics of the traditional power grids are already subject to complex behaviour appearing as a result of the the interplay between dynamics of the nodes and topology, namely synchronisation and cascade effects. When dealing with smart grids, the system complexity increases even more: on top of the physical network of power lines and controllable sources of electricity, the modernisation brings information networks, renewable intermittent generation, market liberalisation, prosumers, among other aspects. In this case, we forecast a dynamical co-evolution of the smart grid and other kind of networked systems that cannot be understood isolated. This review compiles recent results that model electric power grids as complex systems, going beyond pure technological aspects. From this perspective, we then indicate possible ways to incorporate the diverse co-evolving systems into the smart grid model using, for example, network theory and multi-agent simulation.Comment: Submitted to EPJ-ST Power Grids, May 201

IMPROVED AND ROBUST ESTIMATION OF NONRANDOM WAVEFORMS

The problem of estimating nonrandom signal parameters when some a priori information about these parameters is available and when the contaminating noise is not gaussian or is only known in an approximate manner is considered in this work. Utilization of a priori knowledge in the estimation procedures is discussed by describing two general concepts: the minimax method and the generalized Bayes approach. It is seen that for certain kinds of constraints the minimax method provides a solution relatively easy to obtain and one whose mean squared error is smaller than those obtained by more conventional procedures such as the maximum likelihood method. For other types of constraints the generalized Bayes approach utilizing noninformative priors allows incorporation of constraints into the solution of the problem. Often the noninformative priors are not valid probability distribution functions; however, an a posteriori distribution will exist and can, in some sense, be interpreted as an appropriate posteriori distribution. An application of these two methods is illustrated in the estimation of the visual evoked response of the brain to a light stimulus. For cases where the contaminating noise is not gaussian or is only partially specified it is known that optimum procedures, designed under the assumption of exact knowledge of the noise model, can give poor results if the actual model departs even slightly from the assumed one. The main concepts and definitions of robust estimation procedures designed to overcome this problem are then discussed. It is pointed out that asymptotic results are not necessarily good indicators of the performance of the various methods for the small sample size problem and that some procedures, although having desirable properties, may be too complicated to compute for certain applications. A robust algorithm that avoids some of the disadvantages of previously derived methods and is more suitable for certain signal processing applications is presented. When, in addition to the presence of heavy tailed noise, there is knowledge that the signal-to-noise ratio is low it is shown that nonlinear robust procedures can be designed that greatly reduce the mean squared error when compared to linear methods. Several applications of the methods discussed in this work are presented

Radio channel study for colon capsule endoscopy with low-band UWB multiple antenna system

Abstract This paper presents a study of the radio channel characteristics between a colon capsule endoscope and a multiple on-body antenna system in ultra wideband wireless body area networks (UWB-WBAN). The main aim is to study the variation of the channel characteristics for the on-body antennas in different capsule locations throughout the whole colon area. The study is conducted with CST Studio Suite simulations and one of its anatomical voxel models. A simplified capsule model and directive on-body antennas designed for low-band UWB in-body communications are used. It is found that five of this type directive on-body antennas provide sufficient coverage over the whole colon are even in the most challenging capsule locations

Simulation and measurement data-based study on fat as propagation medium in WBAN abdominal implant communication systems

Abstract This paper presents comprehensive study on fat as propagation medium in abdominal implant communication system at low ultrawideband (UWB) frequency range 3.75—4.25 GHz. The main aim is to investigate how signal propagates through visceral and subcutaneous fat layers and how that information can be exploited in implant communication systems. The study is conducted using different methods: electromagnetic simulations, power flow analysis, propagation path calculations and radio channel measurements with animal meat pieces. Simulations are conducted using layer models and anatomical voxel models having different sizes. Results of channel simulations are verified with propagation path calculations. Power flow analysis on cross-cuts of the voxel models is conducted to investigate how the signal propagates inside the tissues. Furthermore, measurements using different animal meat pieces are performed to evaluate the impact of fat constitution on channel characteristics. It is found that similar tendency on fat propagation is seen in the evaluations with different methods. It is also observed that channel attenuation depends not only on the types and thicknesses of the tissues between transmitter and receiver antennas, but also how the tissues, especially fat, is located between the antennas. Channel attenuation difference between different voxels is maximum 14 dB in the studied antenna locations. Furthermore, propagation channel is evaluated with measurements using pork meat having different fat and muscle constitutions. It is found that antenna location respect to fat layers has clear impact on the channel strength although the fat tissue is not directly above the in-body antenna. The difference is noted to be 3–15 dB especially on the side peaks of channel impulse response. The knowledge on fat as a propagation medium is crucial when designing medical monitoring or implant communication systems. Location of antennas/sensor nodes for the monitoring devices can be established so that propagation through fat layer can be exploited

On the UWB in-body propagation measurements using pork meat

Abstract This paper presents a study on the in-body propagation using pork meat at the lower ultrawideband (UWB) frequency band 3.74—4.25 GHz of the wireless body area network (WBAN) standard 802.15.6. Pork meat in terms of the dielectric properties is one of the most similar to human tissues and thus is commonly used in in-body propagation studies. Nevertheless, there are differences in the dielectric properties, creating some differences also in the radio propagation. The first objective of this paper is to investigate by simulations the propagation differences between human and pork tissue layer models. The simulations results show clear differences between the channel characteristics obtained using a human tissues and pork tissues: within the frequency range of interest, the path loss with pork meat can be up to 5 dB less than with the human meat. The second objective of this paper is to study, by measurements, the in-body channel characteristics using different types of pork meat piece having different fat and muscle compositions. It was found that path loss is clearly higher with the pork meat having separate skin, fat, and muscle layers compared to the pork meat having interlaced fat and muscle layers. Furthermore, the third objective of this paper is to study the impact of the meat temperature on the measured channel characteristics by comparing the channels obtained with the meat at the temperatures of 12 °C and at 37 °C. Also, in this case clear differences were observed in path loss: within the frequency range of interest, the path loss was maximum 5 dB lower with meat at 37 °C than with a colder meat. The results presented in this paper provide useful information and relevant aspects for the in-body propagation studies conducted with pork meat

Wearable flexible antenna for UWB on-body and implant communications

Abstract This paper describes the development and evaluation of an on-body flexible antenna designed for an in-body application, as well as on-body communications at ISM and UWB frequency bands. The evaluation is performed via electromagnetic simulations using the Dassault Simulia CST Studio Suite. A planar tissue layer model, as well as a human voxel model from the human abdominal area, are used to study the antenna characteristics next to human tissues. Power flow analysis is presented to understand the power flow on the body surface as well as within the tissues. Simulation results show that this wearable flexible antenna is suitable for in-body communications in the intestinal area, e.g., for capsule endoscopy, in the industrial, scientific, and medical (ISM) band and at lower ultra-wideband (UWB). At higher frequencies, the antenna is suitable for on-body communications as well as in-body communications with lower propagation depth requirements. Additionally, an antenna prototype has been prepared and the antenna performance is verified with several on-body measurements. The measurement results show a good match with the simulation results. The novelty of the proposed antenna is a compact size and the flexible substrate material, which makes it feasible and practical for several different medical diagnosis and monitoring applications

Propagation study of UWB capsule endoscope with multiple on-body antennas

Abstract This paper presents a study of the radio channel characteristics between a capsule endoscopy and a multi on-body antenna system on ultra wideband wireless body area networks (UWB-WBAN). Multiple on-body antennas are required to provide reliable communication link between the capsule and the on-body device, but also essential for capsule localization. The main aim is to study the variation of the frequency and time domain channel characteristics for the selected on-body antennas in different capsule locations, including the most challenging capsule locations deep inside the tissues or far away from most of the antennas. This study also evaluates whether five of selected type directive on-body antennas is enough to cover the intestine area thoroughly. The study is conducted with CST Studio Suite simulations and one of its anatomical voxel models. A simplified capsule model and a directive on-body antenna designed for low-band UWB in-body communications are used in this study. It is found that five of this type directive on-body antennas provide sufficient coverage over the intestine area even in the most challenging capsule locations. In certain capsule locations, the variation between the channel attenuations can be significant, over 40 dB within the frequency range of interest, if the capsule is located deep inside the tissues without smooth access to outer fat layer through which the signal could travel easily to different on-body antennas. Instead, if the capsule is located close to the subcutaneous fat layer, the channel attenuation is moderate even for the antennas which are located far from the capsule