Heribert Baldus

Reliable Set-Up of Medical Body-Sensor Networks

Wireless medical body sensor networks enable a new way of continuous patient monitoring, extending the reach of current healthcare solutions. They improve care giving by a flexible acquisition of relevant vital sign data, and by providing more convenience for patients.

A body-fixed-sensor-based analysis of power during sit-to-stand movements

This study presents an analysis of power exertion for lifting the bodys centre of mass (CoM) during rising from a chair. Five healthy young (21-44 years) and 12 healthy older (70-79 years) subjects performed sit-to-stand (STS) movements while data were measured with force-plates underneath chair and feet and motion sensors attached to different locations on the upper and lower trunk. Force-plate-data were used to determine the timing of STS movements and the vertical power for lifting the CoM from a sitting to a standing position. Data of three-dimensional hybrid motion sensors, consisting of accelerometers, gyroscopes and earth-magnetic-field sensors, were used to determine vertical accelerations and power. The comparison of sensor-based estimations of peak power with peak power calculated from force-plate-data demonstrated fair to excellent linear relationships for all sensor locations on the trunk. The best approximation of peak power was obtained by a weighted combination of data measured at different trunk locations. Results of the older subjects were consistent with those of the young subjects performing slow, normal and fast STS movements. The presented approach is relevant for monitoring fall risk and assessment of mobility in older people. Similar approaches for assessing power may be developed for other mobility related activities, such as stair walking, or sports related activities such as jumping.

Human-centric connectivity enabled by body-coupled communications

With the growing number of mobile devices surrounding a persons body, there is an increasing need to connect this electronic equipment efficiently into a wireless body-area network. In this article we review the body-coupled communications technology, which we show to be a viable basis for future BANs. In BCC, the human body is used as a signal propagation medium, which provides a key benefit - the communication is centered around the user and limited to his or her close proximity, that is, this technology provides human-centric connectivity. This enables unique applications that are illustrated in this work. Moreover, we outline the fundamental properties of the BCC technology and provide different trade-offs and challenges for modulation and protocol design. This article also discusses the outlook for BCC and suggests a number of important research topics.

Plug 'n Play Simplicity for Wireless Medical Body Sensors

Wireless medical body sensors are a key technology for unobtrusive health monitoring. The easy setup of such wireless body area networks is crucial to protect the user from the complexity of these systems. But automatically forming a wireless network comprising all sensors attached to the same body is challenging. We present a method for making wireless body-worn medical sensors aware of the persons they belong to by combining body-coupled with wireless communication. This enables a user to create a wireless body sensor network by just sticking the sensors to her body. A personal identifier allows sensors to annotate their readings with a user ID thereby ensuring safety in personal healthcare environments with multiple users.

A Deterministic Pairwise Key Pre-distribution Scheme for Mobile Sensor Networks

Key management is paramount for mobile sensor network (MSN) security. Due to the characteristics of MSNs, key management must enable direct (without intermediaries) key establishment between two arbitrary nodes. We apply combinatorial design theory to pre-distribute Blundo’s polynomials to MSN nodes. This approach is further combined with Liu and Ning polynomial evaluation optimization yet increasing the scalability of polynomials. It also solves the combinatorial design existence problem of Çamtepe and Yener key pre-distribution scheme (KPS) without a decrease in network scalability or resiliency. The analysis in this paper indicates that this scheme has a number of nice properties, including direct pairwise key establishment, which enables authentication, tolerance to node captures, increased scalability and very low computational and communication overhead.

Sensitivity of sensor-based sit-to-stand peak power to the effects of training leg strength, leg power and balance in older adults

Increasing leg strength, leg power and overall balance can improve mobility and reduce fall risk. Sensor-based assessment of peak power during the sit-to-stand (STS) transfer may be useful for detecting changes in mobility and fall risk. Therefore, this study investigated whether sensor-based STS peak power and related measures are sensitive to the effects of increasing leg strength, leg power and overall balance in older adults. A further aim was to compare sensitivity between sensor-based STS measures and standard clinical measures of leg strength, leg power, balance, mobility and fall risk, following an exercise-based intervention. To achieve these aims, 26 older adults (age: 70-84 years) participated in an eight-week exercise program aimed at improving leg strength, leg power and balance. Before and after the intervention, performance on normal and fast STS transfers was evaluated with a hybrid motion sensor worn on the hip. In addition, standard clinical tests (isometric quadriceps strength, Timed Up and Go test, Berg Balance Scale) were performed. Standard clinical tests as well as sensor-based measures of peak power, maximal velocity and duration of normal and fast STS showed significant improvements. Sensor-based measurement of peak power, maximal velocity and duration of normal STS demonstrated a higher sensitivity (absolute standardized response mean (SRM): ≥ 0.69) to the effects of training leg strength, leg power and balance than standard clinical measures (absolute SRM: ≤ 0.61). Therefore, the presented sensor-based method appears to be useful for detecting changes in mobility and fall risk.

Resource-efficient security for medical body sensor networks

Key management is a fundamental service for medical body sensor network (BSN) security. It provides and manages the cryptographic keys to enable essential security services such as confidentiality, integrity and authentication. In the medical context, the design of a key management service must be consistent with the strict operational and security requirements of healthcare as well as with the resource restrictions of BSN technology. The deterministic pairwise key pre-distribution scheme (DPKPS) allows direct pairwise key establishment in sensor networks. We present a consistent key management service for hospital BSNs based on the DPKPS. We also describe a practical implementation specifically adapted to the strict resource-constraints of the popular MICAz sensor platform. Our performance analysis demonstrates that this key management service enables advanced BSN security services at an extremely low-power and low-memory cost

Efficient distributed security for wireless medical sensor networks

Wireless medical sensor networks (MSNs) enable ubiquitous health monitoring of users during their everyday life, at home or at hospital, without restricting their freedom. MSNs improve therefore userspsila wellbeing and help to quickly react during emergency situations. Security is a key requirement to guarantee safety and privacy of MSN users. However, the resource-constrained nature of the sensor nodes and the operational requirements of these networks hinder the use of traditional security methods. This paper presents a lightweight security system allowing for distributed key establishment and access control in MSNs. The heart of our system is founded on the use of polynomial-based key distribution systems. The security system enables lightweight distributed key agreement and verification of cryptographically signed information, e.g., access control roles or identifiers, on medical sensor nodes without the need of public-key cryptography or a central online trust center. As proof-of-concept, we have implemented our security system on a commercial sensor node platform. Our performance and security analysis shows the feasibility of our approach to deploy resilient and robust MSNs.

Sensor-based monitoring of sit-to-stand performance is indicative of objective and self-reported aspects of functional status in older adults

Studies show that body-fixed motion sensors can be used for long-term monitoring of sit-to-stand (STS) performance in older persons. However, it is unclear how sensor-based measures of STS performance relate to functional status in older adults. Therefore, this study investigated the associations between sensor-based STS measures and standard clinical measures of functional status in older adults. Participants (24 females, 12 males; 72-94 years) performed five normal STS movements while wearing motion sensors on the hip and chest. Objective measures were used to assess mobility (Timed-Up-and-Go Test, Five-Times-Sit-to-Stand Test, Stair Walk Test) and quadriceps strength. Self-reported questionnaires were used to assess limitations in activities of daily living (Groningen Activity Restriction Scale) and frailty (Groningen Frailty Indicator). In general, chest STS measures showed a larger number of significant associations and stronger associations with clinical measures than hip STS measures. Chest maximal velocity, chest peak power, chest scaled peak power and chest stabilization phase SD demonstrated significant associations (weak to strong) with all six clinical measures. Noteworthy is that hip stabilization phase SD showed significant associations (weak to moderate) with five clinical measures. In particular chest peak power and chest scaled peak power demonstrated a moderate ability to discriminate between higher and lower functioning individuals (area under the receiver-operating characteristic curve: 0.75-0.90). This study shows that in particular chest STS measures are indicative of objective and self-reported aspects of functional status in older adults. These findings support the clinical relevance of sensor-based monitoring of STS performance in older persons.

The ANGEL WSN Security Architecture

The EU funded ANGEL project focuses on the development and deployment of wireless sensor networks building ambient intelligence systems for assisted-living and personal health monitoring. The provision of security services such as confidentiality and authentication is a fundamental requirement for ANGEL in order to ensure the safety and privacy of the users; the technical realization is challenging due to the high mobility of users accessing a multitude of wireless sensor networks. Our security architecture ensures the secure deployment and efficient, yet secure operation of ANGEL systems. Based on keying-material distribution, we provide a solution for the secure configuration of sensors and gateways. This ensures that users can interact with their system in an easy, transparent and safe way. We further introduce a fast distributed key agreement protocol on top of ZigBee that enables very fast and efficient operation. Performance and security analysis point out the advantages of our new solution.