Bart Braem

A survey on wireless body area networks

The increasing use of wireless networks and the constant miniaturization of electrical devices has empowered the development of Wireless Body Area Networks (WBANs). In these networks various sensors are attached on clothing or on the body or even implanted under the skin. The wireless nature of the network and the wide variety of sensors offer numerous new, practical and innovative applications to improve health care and the Quality of Life. The sensors of a WBAN measure for example the heartbeat, the body temperature or record a prolonged electrocardiogram. Using a WBAN, the patient experiences a greater physical mobility and is no longer compelled to stay in the hospital. This paper offers a survey of the concept of Wireless Body Area Networks. First, we focus on some applications with special interest in patient monitoring. Then the communication in a WBAN and its positioning between the different technologies is discussed. An overview of the current research on the physical layer, existing MAC and network protocols is given. Further, cross layer and quality of service is discussed. As WBANs are placed on the human body and often transport private data, security is also considered. An overview of current and past projects is given. Finally, the open research issues and challenges are pointed out.

A Comprehensive Survey of Wireless Body Area Networks

Recent advances in microelectronics and integrated circuits, system-on-chip design, wireless communication and intelligent low-power sensors have allowed the realization of a Wireless Body Area Network (WBAN). A WBAN is a collection of low-power, miniaturized, invasive/non-invasive lightweight wireless sensor nodes that monitor the human body functions and the surrounding environment. In addition, it supports a number of innovative and interesting applications such as ubiquitous healthcare, entertainment, interactive gaming, and military applications. In this paper, the fundamental mechanisms of WBAN including architecture and topology, wireless implant communication, low-power Medium Access Control (MAC) and routing protocols are reviewed. A comprehensive study of the proposed technologies for WBAN at Physical (PHY), MAC, and Network layers is presented and many useful solutions are discussed for each layer. Finally, numerous WBAN applications are highlighted.

Characterization of On-Body Communication Channel and Energy Efficient Topology Design for Wireless Body Area Networks

Wireless body area networks (WBANs) offer many promising new applications in the area of remote health monitoring. An important element in the development of a WBAN is the characterization of the physical layer of the network, including an estimation of the delay spread and the path loss between two nodes on the body. This paper discusses the propagation channel between two half-wavelength dipoles at 2.45 GHz, placed near a human body and presents an application for cross-layer design in order to optimize the energy consumption of different topologies. Propagation measurements are performed on real humans in a multipath environment, considering different parts of the body separately. In addition, path loss has been numerically investigated with an anatomically correct model of the human body in free space using a 3-D electromagnetic solver. Path loss parameters and time-domain channel characteristics are extracted from the measurement and simulation data. A semi-empirical path loss model is presented for an antenna height above the body of 5 mm and antenna separations from 5 cm up to 40 cm. A time-domain analysis is performed and models are presented for the mean excess delay and the delay spread. As a cross-layer application, the proposed path loss models are used to evaluate the energy efficiency of single-hop and multihop network topologies.

A Low-delay Protocol for Multihop Wireless Body Area Networks

Wireless body area networks (WBANs) form a new and interesting area in the world of remote health monitoring. An important concern in such networks is the communication between the sensors. This communication needs to be energy efficient and highly reliable while keeping delays low. Mobility also has to be supported as the nodes are positioned on different parts of the body that move with regard to each other. In this paper, we present a new cross-layer communication protocol for WBANs: CICADA or Cascading Information retrieval by Controlling Access with Distributed slot Assignment. The protocol sets up a network tree in a distributed manner. This tree structure is subsequently used to guarantee collision free access to the medium and to route data towards the sink. The paper analyzes CICADA and shows simulation results. The protocol offers low delay and good resilience to mobility. The energy usage is low as the nodes can sleep in slots where they are not transmitting or receiving.

The Wireless Autonomous Spanning tree Protocol for Multihop Wireless Body Area Networks

Wireless body area networks (WBANs) have gained a lot of interest in the world of medical monitoring. Current implementations generally use a large single hop network to connect all sensors to a personal server. However recent research pointed out that multihop networks are more energy-efficient and even necessary when applied near the human body with inherent severe propagation loss. In this paper we present a slotted multihop approach to medium access control and routing in wireless body area networks, the wireless autonomous spanning tree protocol or WASP. It uses crosslayer techniques to achieve efficient distributed coordination of the separated wireless links. Traffic in the network is controlled by setting up a spanning tree and by broadcasting scheme messages over it that are used both by the parent and the children of each node in the tree. We analyze the performance of WASP and show the simulation results

A case for research with and on community networks

Community Networks are large scale, self-organized and decentralized networks, built and operated by citizens for citizens. In this paper, we make a case for research on and with community networks, while explaining the relation to Community-Lab. The latter is an open, distributed infrastructure for researchers to experiment with community networks. The goal of Community-Lab is to advance research and empower society by understanding and removing obstacles for these networks and services.

The Need for Cooperation and Relaying in Short-Range High Path Loss Sensor Networks

This paper focuses on the energy efficiency of communication in small-scale sensor networks experiencing high path loss. In particular, a sensor network on the human body or BASN is considered. The energy consumption or network lifetime of a single-hop network and a multi-hop network are compared. We derive a propagation model and a radio model for communication along the human body. Using these models, energy efficiency was studied analytically for a line and a tree topology. Calculations show that single-hop communication is inefficient, especially for nodes far away from the sink. There however, multi-hop proves to be more efficient but closer to the sink hotspots arise. Based on these findings, we propose to exploit the performance difference by either introducing extra nodes in the network, i.e. dedicated relay devices, or by using a cooperative approach or by a combination of both. We show that these solutions increase the network lifetime significantly.

Improving Reliability in Multi-hop Body Sensor Networks

Body sensor networks are an interesting emerging application of wireless sensor networks to improve healthcare and the quality of life. Current research has mainly focused on single-hop networks, although some works clearly show advantages of multi-hop architectures. In this paper, we model probabilistic connectivity in such multi-hop body sensor networks. Instead of using a circular coverage area, a more accurate model is defined based on the path loss along the human body. Further, we propose improvements to CICADA, a cross-layer multi-hop protocol that handles both medium access and the routing of data in BSNs. CICDA is slot-based and uses schemes to allocate these slots. Preliminary results for two reliability improvements are given: randomization of the schemes and repeating the schemes received from a parent node. We show that these improvements positively affect the throughput of the network and lead to fewer retransmissions. In both cases, the energy consumption of the nodes is hardly influenced.

Path loss models for wireless communication channel along arm and torso: measurements and simulations

In this paper, measurements are performed on a real human using two half-wavelength dipoles, considering different parts of the human body separately. Path loss models are developed for the on- body channels along the arm and torso. The measurement results are verified with FDTD (Finite-Difference Time-Domain) simulations, using an anatomically correct configuration of the arms.

A Secure Cross-Layer Protocol for Multi-hop Wireless Body Area Networks

The development of Wireless Body Area Networks (WBANs) for wireless sensing and monitoring of a persons vital functions, is an enabler in providing better personal health care whilst enhancing the quality of life. A critical factor in the acceptance of WBANs is providing appropriate security and privacy protection of the wireless communication. This paper first describes a general health care platform and pinpoints the security challenges and requirements. Further it proposes and analyzes the CICADA-S protocol, a secure cross-layer protocol for WBANs. It is an extension of CICADA, which is a cross-layer protocol that handles both medium access and the routing of data in WBANs. The CICADA-S protocol is the first integrated solution that copes with threats that occur in this mobile medical monitoring scenario. It is shown that the integration of key management and secure, privacy preserving communication techniques within the CICADA-S protocol has low impact on the power consumption and throughput.