Low power body sensor network design based on relaying of creeping waves in the unlicensed 2.4GHz band

Body Sensor Networks are an important enabling technology for future applications in remote medical diagnostics. Practical deployments of these systems have only recently edged closer to viability, due in part to advances in low power electronics and System-On-Chip devices. Wireless communication between these sensors remains a daunting challenge, and designers typically leverage existing industrial standards designed for applications with significantly different communications requirements. This Thesis proposes a wireless communications platform designed specifically for body mounted sensors, exploiting a phenomenon in electromagnetic wave propagation known as a creeping wave. Relaying of these waves leads to a highly reliable body sensor network with very low power consumption in the unlicensed 2.4 GHz band. A link budget is derived based on the creeping wave component of the transmitted signal, which is then used to design a spread spectrum wireless transceiver. Significant attention is given to interference mitigation, allowing the system to co-exist with other wireless devices on the internationally unlicensed band. Fading statistics from both anechoic and high multipath scenarios are used to define a channel model for the system. The link budget and channel model lead to the proposed use of relaying as a power savings technique, and this concept is a core feature of the design. This technique is shown to provide reliable total body coverage with very low transmission power, a result that has eluded body sensor networks to date. Various relaying topologies are discussed, and robust operation for highly mobile users is achieved via sensor handoffs, a concept that resembles a similar solution in cellular networks. The design extends to define a polling protocol and packet structures. Objective performance metrics are defined, and the proposed system is evaluated in line with these metrics. The power reduction of the suggested approach is analyzed by comparing the network lifetime and energy-per-bit to those of a reference system offering the same quality of service without relaying. The analysis results in generic closed form expressions of significant gains. The improvement in network lifetime increases with the number of sensors and settles at approximately 8x104, 7x106, 7x107 and 3x108 for 2,4,6 and 8 relaying nodes respectively. The energy-per-bit is shown to decrease by 2, 116, 828 and 2567 for 2, 4, 6 and 8 relay nodes respectively

SIMPLE: Stable Increased-throughput Multi-hop Protocol for Link Efficiency in Wireless Body Area Networks

In this work, we propose a reliable, power efficient and high throughput routing protocol for Wireless Body Area Networks (WBANs). We use multi-hop topology to achieve minimum energy consumption and longer network lifetime. We propose a cost function to select parent node or forwarder. Proposed cost function selects a parent node which has high residual energy and minimum distance to sink. Residual energy parameter balances the energy consumption among the sensor nodes while distance parameter ensures successful packet delivery to sink. Simulation results show that our proposed protocol maximize the network stability period and nodes stay alive for longer period. Longer stability period contributes high packet delivery to sink which is major interest for continuous patient monitoring.Comment: IEEE 8th International Conference on Broadband and Wireless Computing, Communication and Applications (BWCCA'13), Compiegne, Franc

Experimental investigation into novel methods of reliable and secure on-body communications with low system overheads

Until recently the concept of wearable biosensors for purposes of medical monitoring was restricted to wired sensor applications. Recent advances in electronics and wireless communications have made the possibility of removing the wire from sensor applications a possibility. These advances have led to the development of small scale, wearable, sensing and communication platforms that can be placed on the human body creating the foundation for a Body Sensor Network (BSN). Body Sensor Networks aim to remove the restrictions that traditional wired sensors impose. The anticipation is that BSNs will permit the monitoring of physiological signals in any environment without limitation, giving Physicians the ability to monitor patients more closely and in environments that they cannot monitor today. Even with the recent advancements of electronics and wireless communications there are still many unanswered questions for practical solutions of BSNs that prevent BSNs from replacing traditional wired systems altogether. There is a great need for research into BSN architectures to set the standard for wireless sensor monitoring. In this work a development platform has been created for the investigation into the design and implementation of practical BSN solutions. The platform is used to compare BSN architectures and provide quantifiable results. From this work BSN architecture components that provide optimizations in system performance, energy, network lifetime and security are recommended. In Chapter 3 BSN network architectures employing the use of relaying of creeping waves is investigated. The investigation includes experimental analysis of various test environments. Experimentation demonstrates that the relaying of creeping waves offers considerable performance gains when compared to non-relay networks. For example, relaying is shown to increase network-lifetime by a factor of 13, decrease energy-per-bit requirements by 13 dB and provide the ability for the network to compensate for considerably wider fade margins. In Chapter 4 utilizing the randomness of the wireless channel for securing on-body communications with low overheads is considered. A low-complexity algorithm for establishing symmetric encryption keys is presented and validated. The algorithm relies on readily available RSSI measurements obtained from existing packets being sent and received in the network. The generated bit sequences from the algorithm are evaluated for matching between two communicating parties and mismatching with a malicious eavesdropper. It is shown that the algorithm produces long sequences of highly random bits that are perfectly matched between legitimate parties and highly mismatched with the eavesdropper

Wireless body area network platform utilizing energy-efficient routing of physiological data

Wireless Body Area Networks (WBANs) consist of several wireless sensors located around a human body. These sensors may measure several biological signals, movement, and temperature. Due to major improvements in power consumption and constantly shrinking devices, WBANs are becoming ubiquitous. As a side effect present because of the small form factor of these devices, the battery size is limited. While the sensors themselves may be extremely power efficient, all of the measured data must be transmitted over a much less efficient wireless link. One benefit of WBANs is that they rarely include more than a dozen wireless devices over a small area. This constraint allows for the use of routing techniques not suitable for larger wireless sensor networks(WSNs). Presented in this work is a novel global routing algorithm link-cost function to maximize network lifetime in WBANs. Also included are a basic software framework for developing WBANs, a sample Wireless Electrocardiogram (ECG) application, and a simple link cost algorithm development platform

AN ENHANCED-SIMPLE PROTOCOL FOR WIRELESS BODY AREA NETWORKS

A Wireless Body Sensor Network (WBSN) characterizes an independent system that is used for the purpose of monitoring the daily routine activities of an individual. It comprises of smart sensor nodes which do not have any kind of adverse effect on the daily routine activities and are quite effective in the detection of chronic health problems such as diabetes, heart attack, asthma etc., and to caution the person suffering from diseases in the case of an emergency conditions. In this work, a wireless body area network routing protocol is designed where distance of the sink from various nodes and residual energy of the nodes decides the forwarding nodes to maximize the throughput. In this work, all the sensors on the body will transfer data to sink node and sink node will transmit data to base station or to the server. The simulation results will be evaluated in terms of remaining energy, throughput and number of dead nodes. The obtained results are also ompared with recent published protocols and it has been found that in comparison to SIMPLE and iM-SIMPLE, the proposed protocol E2 (nomenclature used in the paper) has throughput higher than 12.46% and 6.7% respectively

Fast design space exploration of vibration-based energy harvesting wireless sensors

An energy-harvester-powered wireless sensor node is a complicated system with many design parameters. To investigate the various trade-offs among these parameters, it is desirable to explore the multi-dimensional design space quickly. However, due to the large number of parameters and costly simulation CPU times, it is often difficult or even impossible to explore the design space via simulation. This paper presents a response surface model (RSM) based technique for fast design space exploration of a complete wireless sensor node powered by a tunable energy harvester. As a proof of concept, a software toolkit has been developed which implements the proposed design flow and incorporates either real data or parametrized models of the vibration source, the energy harvester, tuning controller and wireless sensor node. Several test scenarios are considered, which illustrate how the proposed approach permits the designer to adjust a wide range of system parameters and evaluate the effect almost instantly but still with high accuracy. In the developed toolkit, the estimated CPU time of one RSM estimation is 25s and the average RSM estimation error is less than 16.5

Energy Efficient Sensor Nodes Powered by Kinetic Energy Harvesters – Design for Optimum Performance

In an energy harvester powered wireless sensor node system, as the energy harvester is the only energy source, it is crucial to configure the microcontroller and the sensor node so that the harvested energy is used efficiently. This paper outlines modelling, performance optimisation and design exploration of the complete, complex system which includes the analogue mechanical model of a tunable kinetic microgenerator, its magnetic coupling with the electrical blocks, electrical power storage and processing parts, the digital control of the microgenerator tuning system, as well as the power consumption models of sensor node. Therefore not only the energy harvester design parameters but also the sensor node operation parameters can be optimised in order to achieve the best system performance. The power consumption models of the microcontroller and the sensor node are built based on their operation scenarios so that the parameters of the digital algorithms can be optimised to achieve the best energy efficiency. In the proposed approach, two Hardware Description Languages, VHDL-AMS and SystemC-A is used to model the system's analogue components as well as the digital control algorithms which are implemented in the microcontroller and the sensor node. Simulation and performance optimisation results are verified experimentally. In the development of the fast design exploration tool based on the response surface technique, the response surface model (RSM) is constructed by carrying out a series of simulations. The RSM is then optimised using MATLAB's optimisation toolbox and the optimisation results are presented

Wireless Links for Telecare and Telemedicine Applications using Compact Body-Worn Antennas.

PhDThis thesis concerns the design of body-centric wireless communications for short-range indoor Telecare/Telemedicine applications. Such communications are starting to be used to convey key, relatively low data-rate body-sensor data wirelessly between on-body sensor node(s) located on potentially mobile clients/patients and fixed off-body Access Point(s). From the outset, key practical considerations/constraints were assumed; in particular that, wherever possible, existing components (including antennas) and established protocols would be employed. This approach should enable existing manufacturers of mobile wireless components to rapidly adapt to the potential Telecare/Telemedicine market segment with minimum R&D capital outlay. In addition, maximum user convenience of the on-body nodes has been taken into account to ensure that they are readily accepted and hence actually used. As anticipated, using existing mobile antennas (designed for nominally free space use) in close proximity to the human body poses several limitations. These are quantified here for a particular candidate commercial device. In the process, however, a novel unanticipated effect of the nearby body was also discovered; namely that the body completely depolarises the (otherwise reasonably polarised) antenna patterns. A potential physical explanation for this effect is identified and evaluated by means of analysis based on a modified Geometric Optics approach. The result of this analysis agrees with those simulated and measured here to remarkable accuracy. The thesis then presents several multi-antenna schemes to overcome these severe limitations and identifies that best suited to the indoor Telecare/Telecommunication application here. Simulations at the Physical Layer are reported with this optimum Wireless Links for Telecare and Telemedicine using Compact Body-Worn Antennas 8 single-input multiple-output (SIMO) antenna scheme for a typical indoor scenario. These quantify the overall system performance when such measures are adopted, demonstrating that it is adequate in this role. Finally, promising techniques are suggested for Future Work which could afford further significant system improvements for future upgrades of the solution presented here. In particular, the use of metamaterial techniques are indicated which could substantially reduce on-body transmit powers currently required. This would give highly desirable increases in battery lifetimes for the mobile battery powered on-body nodes.Engineering and Physical Science Research Council (EPSRC

Towards reliable communication in low-power wireless body area networks

Es wird zunehmend die Ansicht vertreten, dass tragbare Computer und Sensoren neue Anwendungen in den Bereichen Gesundheitswesen, personalisierte Fitness oder erweiterte Realität ermöglichen werden. Die am Körper getragenen Geräte sind dabei mithilfe eines Wireless Body Area Network (WBAN) verbunden, d.h. es wird drahtlose Kommunikation statt eines drahtgebundenen Kanals eingesetzt. Der drahtlose Kanal ist jedoch typischerweise ein eher instabiles Kommunikationsmedium und die Einsatzbedingungen von WBANs sind besonders schwierig: Einerseits wird die Kanalqualität stark von den physischen Bewegungen der Person beeinflusst, andererseits werden WBANs häufig in lizenzfreien Funkbändern eingesetzt und sind daher Störungen von anderen drahtlosen Geräten ausgesetzt. Oft benötigen WBAN Anwendungen aber eine zuverlässige Datenübertragung. Das erste Ziel dieser Arbeit ist es, ein besseres Verständnis dafür zu schaffen, wie sich die spezifischen Einsatzbedingungen von WBANs auf die intra-WBAN Kommunikation auswirken. So wird zum Beispiel analysiert, welchen Einfluss die Platzierung der Geräte auf der Oberfläche des menschlichen Körpers und die Mobilität des Benutzers haben. Es wird nachgewiesen, dass während regelmäßiger Aktivitäten wie Laufen die empfangene Signalstärke stark schwankt, gleichzeitig aber Signalstärke-Spitzen oft einem regulären Muster folgen. Außerdem wird gezeigt, dass in urbanen Umgebungen die Effekte von 2.4 GHz Radio Frequency (RF) Interferenz im Vergleich zu den Auswirkungen von fading (Schwankungen der empfangenen Signalstärke) eher gering sind. Allerdings führt RF Interferenz dazu, dass häufiger Bündelfehler auftreten, d.h. Fehler zeitlich korrelieren. Dies kann insbesondere in Anwendungen, die eine geringe Übertragungslatenz benötigen, problematisch sein. Der zweite Teil dieser Arbeit beschäftigt sich mit der Analyse von Verfahren, die potentiell die Zuverlässigkeit der Kommunikation in WBANs erhöhen, ohne dass wesentlich mehr Energie verbraucht wird. Zunächst wird der Trade-off zwischen Übertragungslatenz und der Zuverlässigkeit der Kommunikation analysiert. Diese Analyse basiert auf einem neuen Paket-Scheduling Algorithmus, der einen Beschleunigungssensor nutzt, um die WBAN Kommunikation auf die physischen Bewegungen der Person abzustimmen. Die Analyse zeigt, dass unzuverlässige Kommunikationsverbindungen oft zuverlässig werden, wenn Pakete während vorhergesagter Signalstärke-Spitzen gesendet werden. Ferner wird analysiert, inwiefern die Robustheit gegen 2.4 GHz RF Interferenz verbessert werden kann. Dazu werden zwei Verfahren betrachtet: Ein bereits existierendes Verfahren, das periodisch einen Wechsel der Übertragungsfrequenz durchführt (channel hopping) und ein neues Verfahren, das durch RF Interferenz entstandene Bitfehler reparieren kann, indem der Inhalt mehrerer fehlerhafter Pakete kombiniert wird (packet combining). Eine Schlussfolgerung ist, dass Frequenzdiversität zwar das Auftreten von Bündelfehlern reduzieren kann, dass jedoch die statische Auswahl eines Kanals am oberen Ende des 2.4 GHz Bandes häufig schon eine akzeptable Abhilfe gegen RF Interferenz darstellt.There is a growing belief that wearable computers and sensors will enable new applications in areas such as healthcare, personal fitness or augmented reality. The devices are attached to a person and connected through a Wireless Body Area Network (WBAN), which replaces the wires of traditional monitoring systems by wireless communication. This comes, however, at the cost of turning a reliable communication channel into an unreliable one. The wireless channel is typically a rather unstable medium for communication and the conditions under which WBANs have to operate are particularly harsh: not only is the channel strongly influenced by the movements of the person, but WBANs also often operate in unlicensed frequency bands and may therefore be exposed to a significant amount of interference from other wireless devices. Yet, many envisioned WBAN applications require reliable data transmission. The goals of this thesis are twofold: first, we aim at establishing a better understanding of how the specific WBAN operating conditions, such as node placement on the human body surface and user mobility, impact intra-WBAN communication. We show that during periodic activities like walking the received signal strength on an on-body communication link fluctuates strongly, but signal strength peaks often follow a regular pattern. Furthermore, we find that in comparison to the effects of fading 2.4 GHz Radio Frequency (RF) interference causes relatively little packet loss - however, urban 2.4 GHz RF noise is bursty (correlated in time), which may be problematic for applications with low latency bounds. The second goal of this thesis is to analyze how communication reliability in WBANs can be improved without sacrificing a significant amount of additional energy. To this end, we first explore the trade-off between communication latency and communication reliability. This analysis is based on a novel packet scheduling algorithm, which makes use of an accelerometer to couple WBAN communication with the movement patterns of the user. The analysis shows that unreliable links can often be made reliable if packets are transmitted at predicted signal strength peaks. In addition, we analyze to what extent two mechanisms can improve robustness against 2.4 GHz RF interference when adopted in a WBAN context: we analyze the benefits of channel hopping, and we examine how the packet retransmission process can be made more efficient by using a novel packet combining algorithm that allows to repair packets corrupted by RF interference. One of the conclusions is that while frequency agility may decrease "burstiness" of errors the static selection of a channel at the upper end of the 2.4 GHz band often already represents a good remedy against RF interference