Nick Timmons

An adaptive energy efficient MAC protocol for the medical body area network

Medical body area networks will employ both implantable and bodyworn devices to support a diverse range of applications with throughputs ranging from several bits per hour up to 10 Mbps. The challenge is to accommodate this range of applications within a single wireless network based on a suitably flexible and power efficient medium access control protocol. To this end, we present a Medical Medium Access Control (MedMAC) protocol for energy efficient and adaptable channel access in body area networks. The MedMAC incorporates a novel synchronisation mechanism and initial power efficiency simulations show that the MedMAC protocol outperforms the IEEE 802.15.4 protocol for two classes of medical applications.

An energy analysis of IEEE 802.15.6 scheduled access modes

Body Area Networks (BANs) are an emerging area of wireless personal communications. The IEEE 802.15.6 working group aims to develop a communications standard optimised for low power devices operating on, in or around the human body. IEEE 802.15.6 specifically targets low power medical application areas. The IEEE 802.15.6 draft defines two main channel access modes; contention based and contention free. This paper examines the energy lifetime performance of contention free access and in particular of periodic scheduled allocations. This paper presents an overview of the IEEE 802.15.6 and an analytical model for estimating the device lifetime. The analysis determines the maximum device lifetime for a range of scheduled allocations. It also shows that the higher the data rate of frame transfers the longer the device lifetime. Finally, the energy savings provided by block transfers are quantified and compared to immediately acknowledged alternatives.

Microstrip-Fed Pattern- and Polarization- Reconfigurable Compact Truncated Monopole Antenna

A microstrip-fed truncated monopole antenna with radiation pattern and polarization reconfigurability is presented. The antenna fabricated on a substrate of dielectric constant 4.4 and thickness 1.6 mm is highly compact with an overall dimension of only 0.25λs × 0.25λs. The pattern of the antenna is omnidirectional and is reconfigurable with the polarization in the orthogonal planes. The proposed antenna is suitable for 2.4-GHz wireless applications with a bandwidth of 95 MHz. The measured gain of the antenna is -1.1 dBi at the resonant frequency. The simulation (Ansoft HFSS) and measurement (R&S ZVB8 Vector Network Analyzer) results are also discussed.

An energy analysis of IEEE 802.15.6 scheduled access modes for medical applications

Body Area Networks (BANs) are an emerging area of wireless personal communications. The IEEE 802.15.6 working group aims to develop a communications standard optimised for low power devices operating on, in or around the human body. IEEE 802.15.6 specifically targets low power medical application areas. The IEEE 802.15.6 draft defines two main channel access modes; contention based and contention free. This paper examines the energy lifetime performance of contention free access and in particular of periodic scheduled allocations. This paper presents an overview of the IEEE 802.15.6 and an analytical model for estimating the device lifetime. The analysis determines the maximum device lifetime for a range of scheduled allocations. It also shows that the higher the data rate of frame transfers the longer the device lifetime. Finally, the energy savings provided by block transfers are quantified and compared to immediately acknowledged alternatives.

The effect of body shape and gender on wireless Body Area Network on-body channels

Technological advancements have made possible the emergence of Body Area Networks (BANs). There are numerous on-body channel characterizations in the literature performed on a phantom or a single human subject. In this paper, using multiple subjects, we consider the effect of body shape and gender on the on-body channel. A characterization of a narrowband on-body to on-body channel among different subjects is presented. The paper investigates the relationship between the propagation and the subjects physical characteristics. The investigation is performed at 2360 MHz; the new medical band undergoing FCC approval. Our results show that the path loss in women is less than that in men and the level of fade is usually higher in men than women. They also show that involuntary movements along with respiration cause small-scale fading that follows the Rice distribution.

Improving the ultra-low-power performance of IEEE 802.15.6 by adaptive synchronisation

In ultra-low data rate wireless sensor networks (WSNs) waking up just to listen to a beacon every superframe can be a major waste of energy. This study introduces MedMAC, a medium access protocol for ultra-low data rate WSNs that achieves significant energy efficiency through a novel synchronisation mechanism. The new draft IEEE 802.15.6 standard for body area networks includes a sub-class of applications such as medical implantable devices and long-term micro miniature sensors with ultra-low power requirements. It will be desirable for these devices to have 10 years or more of operation between battery changes, or to have average current requirements matched to energy harvesting technology. Simulation results are presented to show that the MedMAC allows nodes to maintain synchronisation to the network while sleeping through many beacons with a significant increase in energy efficiency during periods of particularly low data transfer. Results from a comparative analysis of MedMAC and IEEE 802.15.6 MAC show that MedMAC has superior efficiency with energy savings of between 25 and 87% for the presented scenarios.

On-body to on-body channel characterization

Interest in on-body communication channels is growing as the use of wireless devices increases in medical, consumer and military sensor applications. This paper presents an experimental investigation and analysis of the narrowband on-body propagation channel. This analysis considers each of the factors affecting the channel during a range of stationary and motion activities in different environments with actual wireless mote devices on the body. Use of such motes allows greater freedom in the subjects movements and the inclusion of real-world indoor and outdoor environments in a test sequence. This paper identifies and analyses the effect of the different components of the signal propagation (mean propagation path gain, large-scale fading and small-scale fading) and the cause of the losses and variation due to activities, positions or environmental factors. Our results show the effect on the received signal and the impact of voluntary and involuntary movements, which cause shadowing effects. The analysis also allows us to identify sensor positions on the body that are more reliable and those positions that may require a relay or those that may be suitable for acting as a relay.

Current characterisation for ultra low power wireless body area networks

The emerging area of body area networks (BAN) imposes challenging requirements on hardware and software to achieve the desired lifetimes for certain devices such as long term medical implants. In this paper, we propose a novel approach to the measurement and characterisation of the energy consumption of BAN devices. The approach uses a low cost energy auditing circuit and addresses the problem of accurately measuring low-level current consumption. This new technique will allow precise and analytical measurements of systems and components in terms of energy. This will help circuit designers minimise power consumption in BAN devices. Software engineers might use this approach to validate and optimise embedded code. Network engineers can optimise network parameters to reduce the power consumption of a single node. Adoption of the proposed technique will aid the development of ultra-low power wireless BANs. Results are presented on current characterisation for two wireless motes.

Analysis of the Effect of Human Presence on a Wireless Sensor Network

Wireless Sensor Networks (WSNs) are gaining an increasing industry wide adoption. However, there remain major challenges such as network dimensioning and node placement especially in Built Environment Networks (BENs). Decisions on the node placement, orientation, and the number of nodes to cover the area of interest are usually ad-hoc. Ray tracing tools are traditionally employed to predict RF signal propagation; however, such tools are primarily intended for outdoor environments. RF signal propagation varies greatly indoors due to building materials and infrastructure, obstacles, node placement, antenna orientation and human presence. Because of the complexity of signal prediction, these factors are usually ignored or given little weight when such networks are analyzed. The papers results show the effects of the building size and layout, building materials, human presence and mobility on the signal propagation of a BEN. Additionally, they show that antenna radiation pattern is a key factor in the RF propagation performance, and appropriate device orientation and placement can improve the network reliability. Further, the RSS facility in RF transceivers can be exploited to detect the presence and motion of humans in the environment.

A schema for the selection of network topology for Wireless Body Area Networks

A topology governs the logical connectivity between the nodes in the network. Development of Wireless Body Area Networks (WBANs) requires applying tailored technologies to countermeasure the effects of wireless propagation while satisfying constrains imposed by hardware. Important part of this process is topology selection as it affects the development of the entire network protocol stack. For example, use of a star or point-to-point topology removes the need for using routing as required by other topologies such as mesh. Therefore in this paper we propose a novel method of topology selection for BANs that we refer to as a topology selection schema. The schema identifies and discusses a broad range of parameters that should be considered in topology selection and then proposes a topology selection schema. The schema determines the values of those parameters by comparing them against a given set of assumptions on the use of the network, e.g. use case scenario, environmental conditions, device and traffic related parameters. Then it reduces them into a set of concise parameters, which can be easily used to assess the suitability of given topologies.