Publications with abstracts

We present the design and initial evaluation of a mobile gait analysis system, SensorShoe. The target user group is represented by Parkinson’s Disease patients, which need continuous assistance with the physical therapy in their home environment. SensorShoe analyses the gait by using a low-power sensor node equipped with movement sensors. In addition, SensorShoe gives real-time feedback and therapy assistance to the patient, and provides the caregivers an effective remote monitoring and control tool.

We propose a method through which dynamic sensor nodes determine that they move together by communicating and correlating their movement information. We describe two possible solutions, one using inexpensive tilt switches, and another one using low-cost MEMS accelerometers. We implement a fast, incremental correlation algorithm, which can run on resource constrained devices. The tests with the implementation on real sensor nodes show that the method distinguishes between joint and separate movements. In addition, we analyse the scalability from four different perspectives: communication, energy, memory and execution speed. The solution using tilt switches proves to be simpler, cheaper and more energy efficient, while the accelerometer-based solution is more accurate and more robust to sensor alignment problems.

Sensor nodes can autonomously form ad-hoc groups based on their common context. We propose a solution for grouping sensor nodes attached on the same vehicles on wheels. The nodes periodically receive the movement data from their neighbours and calculate the correlation coefficients over a time history. A high correlation coefficient implies that the nodes are moving together. We demonstrate the algorithm using two types of movement sensors: tilt switches and MEMS accelerometers. We place the nodes on two wirelessly controlled toy cars, and we observe in real-time the group membership via the LED colours of the nodes. In addition, a graphical user interface running on the base station shows the movement signals over a recent time history, the latest sampled data, the correlation between each two nodes and the group membership.

We propose an energy-efficient service discovery protocol for wireless sensor networks. Our solution exploits a cluster overlay, where the clusterhead nodes form a distributed service registry. A service lookup results in visiting only the clusterhead nodes. We aim for minimizing the communication costs during discovery of services and maintenance of a functional distributed service registry. We compare theoretically and by simulation the impact of the chosen clustering algorithm on the service discovery protocol.

Currently, most wireless sensor network applications assume the presence of single-channel Medium Access Control (MAC) protocols. When sensor nodes are densely deployed, single-channel MAC protocols may be inadequate due to the higher demand for the limited bandwidth. To overcome this drawback, we propose multiple channel support for improving the performance. Our method allows the nodes to utilize new frequency channels which results in the significant increase on the number of nodes that are granted access to the wireless medium. The method requires only one half-duplex transceiver per node, which is capable of sending and receiving over distinguished frequency channels. Simulation results show that, method successfully utilizes multiple channels and increases the performance proportional to the number of available frequencies for an example single-channel MAC protocol, LMAC.

Wireless sensor networks are used to perform sensor measurements under a variety of conditions. In settings with sparse distribution of sensor nodes, multi-hop routing is traditionally used to forward information from a source node to a destination node. A problem with this approach is that loss of connectivity of nodes in the path between source and destination may lead to a partitioning of the network. We present cooperative transmission to connect previously disconnected parts of a network thus overcoming the separation problem of multi-hop networks. We show that this approach improves connectivity over 50 of nodes necessary to provide full coverage of an area up to 30 The paper presents theory, a comparison of 3 types of cooperative transmission approaches to multi-hop networks and shows the practical feasibility by presenting a prototypical implementation on the Particle Computer wireless sensor node platform.

Cooperative transmission follows the idea to achieve better reception quality for wireless communication systems by exploiting spatial diversity. We discuss the case where a group of sensor nodes transmit cooperatively and simultaneously identical symbols to a far destination. Doing so, they achieve a higher total transmit power. This is useful to reach destinations when no intermediate relays are able to act as repeater. We discuss this situation under the constraints of low power and low cost hardware and derive an optimal symbol constellation for a M-ary modulation scheme to minimize the symbol error. For this, we assume neither phase nor carrier synchronization between cooperatively transmitting nodes or the receiver yielding an easy to implement system with very low requirements for the participating wireless sensor nodes. Transmitted signals superimpose non-coherently in the receiver which uses only the amplitude information to decode symbols acting as an energy detector. We therefore name this modulation Energy Shift Keying (ESK).

Energy has become one of the main cost drivers in our society. Therefore technical systems and solutions that save energy and keep the costs down gain in importance. In buildings, equipment like air-condition and heating consume high amounts of energy. Even small adjustments can therefore lead to significant lowering of costs. With the help of sensor networks, the monitoring and controlling of facilities can be simplified and improved. In this demo, we present a fine granular and long-term operating system for monitoring the relevant physical parameters of a building both indoors and outdoors.

In the last few years, WLAN has seen immense growth and it will continue this trend due to the fact that it provides convenient connectivity as well as high speed links. Furthermore, the infrastructure already exists in most public places and is cheap to extend. These advantages, together with the fact that WLAN covers a large area and is not restricted to line of sight, have led to developing many WLAN localization techniques and applications based on them. In this paper we present a novel calibration-free localization technique using the existing WLAN infrastructure that enables conference participants to determine their location without the need of a centralized system. The evaluation results illustrate the superiority of our technique compared to existing methods.

In addition, we present a privacy observant architecture to share location information. We handle both the location of people and the resources in the infrastructure as services, which can be easily discovered and used. An important design issue for us was to avoid tracking people and giving the users control over who they share their location information with and under which conditions.

This paper introduces CODE, a Description Language for Wireless Collaborating Objects (WCOs), with the specific aim of enabling service management in smart environments. WCOs extend the traditional model of wireless sensor networks by transferring additional intelligence and responsibility from the gateway level to the network. WCO are able to offer complex services based on cooperation among sensor nodes. CODE provides the vocabulary for describing the complex services offered by WCO. It enables description of services offered by groups, on-demand services, service interface and sub-services. The proposed methodology is based on XML, which is widely used for structured information exchange and collaboration. CODE can be directly implemented on the network gateway, while a lightweight binary version is stored and exchanged among sensor nodes. Experimental results show the feasibility and flexibility of using CODE as a basis for service management in WCO.

In this paper, we describe an implementation of FLAVOUR (Friendly Location-aware conference Assistant with priVacy Observant architectURe), in which people/infrastructure resources act as individual service providers offering their location as a service. By subscribing to this service, in the one hand, conference participants can be aware of each others whereabouts as well as being able to chat. On the other hand, conference organizers can notify interested attendants about special events such as cancellation of a track or change in the presentation rooms. The presented architecture uses existing WLAN infrastructure for cost efficiency, and uniquely incorporates the location information as a service into Jini service discovery platform. Location itself is determined with high accuracy by using a calibration free technique.

This paper presents a new collaborative mechanism for efficient coordination of radio communication devices, in particular addressing the unlicensed ISM band at 2.4 GHz. As the traffic in the ISM band is increasing tremendously, the potential for interference between uncoordinated devices is becoming a problem and can result in severe degradation of the performance of these systems. Devices using the same technology can benefit from standardized QoS solution, as for example introduced in WLAN IEEE Some recent 802.11e [ 1]. But the unlicensed ISM typically supports heterogeneous networks using different technologies. Collaborative and non-collaborative mechanisms that have been proposed are designed only for some particular systems and are inefficient because they result in a lack of a spectrum map. The collaborative mechanism proposed in this paper enables spectrum coordination between multiple wireless devices using conventional radio standards such as IEEE WLAN 802.11x, Bluetooth, ZigBee, and so on. The proposed mechanism permits flexibility in spectrum sharing procedures, which can take into account more complex parameters and results in a more efficient spectrum allocation. The collaborative mechanism is based on a Shared Broadcast Control Channel (SBCH). The SBCH is a low rate signal using continuous phase modulation. Simulation results show that the SBCH signal can be generated by conventional transmitters and can be detected with conventional receivers.

This paper presents the ìPart wireless sensor system especially designed for settings requiring a high population of sensors. Those settings can be found in actual research of indoor activity recognition and ambient intelligence as well as outdoor environmental monitoring. ìParts are very small sensor nodes (10x10mm), with wireless communication, enabling the setup of high density networks at low cost and with a long life time. Basic configuration capabilities like sensor type and sampling rate provide enough flexibility while keeping the system easy to deploy and affordable at the same time.

This thesis describes the research conducted on algorithms for wireless sensor networks

that are applicable for fine-grained localisation in a small indoor environment.

The goal of our project is to provide location information about mobile sensor

nodes that is accurate enough to be used for activity recognition of the persons

carrying the nodes. The scalability of existing localisation algorithms, designed

for outdoor and large indoor environments, is investigated. Our preliminary experiments

show that algorithms based on radio signal strength should provide satisfactory

results for small-scale indoor localisation. Two localisation systems based

on radio signal strength were therefore designed and implemented: a fingerprinting

system and a proximity-based system. The experiments that were conducted

to test the systems show that the localisation errors achieved by the fingerprinting

system are variable, and therefore that the system is unreliable, whereas the proximity

system produces accurate, relative location information. Consequently, only

the proximity solution is applicable for the activity recognition problem, although

minor improvements to the system are still necessary.

Knowledge of the fine-grained location and orientation of devices on a surface can be used to enhance the surface-based computing tasks of mobile users in the home and workplace. However, existing systems which provide surface-based positioning information are often not a practical solution for mobile users, since the systems all rely upon pre-installed and calibrated environmental infrastructure. In this paper, we present prototype positioning devices for surfaces which do not rely on such infrastructure. We show that inexpensive infrared transducers can be used to effectively sense relative location and orientation of surface devices. We evaluate the novel approach of using intensity of light pulses for fine-grained location measurements.

Service discovery is an emerging field in the area of ubiquitous computing. There are various techniques and protocols (proposed or/and already implemented) particularly tailored to specific sets of objectives. This paper analyses the current state of the art and presents a taxonomy of service discovery protocols. Along with design issues, the diversity of solutions and open questions are systematically studied.

The ordering of messages according to a given time measure is a largely discussed topic. Nevertheless, wireless or wired systems considering the order of messages do not use the access layer to accomplish this task. In this paper, we discuss the use of non-destructive bit-wise arbitration on the MAC layer for real-time message ordering in wireless sensor networks. With this access method, it is possible to use the measure of elapsed waiting time of a message as an input parameter to the channel access. Through the use of adaptive priorities, messages carrying older information get higher priorities and can therefore gather access ¯rst. This hard real-time message ordering mechanism realizes message ordering for one-hop distance mesh topologies. Additionally it is an ideal basis for message-ordering transport protocols. We discuss the system in the parameter context of WiFi (IEEE 802.11a) and Zigbee (IEEE 802.15.4) and successfully implemented the access method on a wireless sensor network.

The retail store environment is a challenging application area for Pervasive Computing technologies. It has demanding base conditions due to the number and complexity of the interdependent processes involved. We present first results of an ongoing study with dm-drogerie markt, a large chemist’s retailer, that indicate that supporting product monitoring tasks with novel pervasive technology is useful but still needs technical advances. Based on this study, we uncover problems that occur when using identification technology (such as RFID) for product monitoring. The individual identification struggles with data overload and inefficient channel access due to the high number of tags involved. We address these problems with the concept of Radio Channel Computing, combining approaches from information theory, such as the method of types and multiple access adder channels. We realise data pre-processing on the physical layer and significantly improve response time and scalability. With mathematical formulation, simulations and a real world implementation, we evaluate and prove the usefulness of the proposed system.

In this paper we identify the common techniques and technologies that are enabling location identification in a ubiquitous computing environment. We also address the important parameters for evaluating such systems. Through this survey, we explore the current trends in commercial products and research in the area of localization. Although localization is an old concept, further research is needed to make it really usable for ubiquitous computing. Therefore, we indicate future research directions and address localization in the framework of our Smart Surroundings project.

This paper presents a sensor-based, networked embedded system, referred to as the Particle computer system. It is comprised of tiny wireless sensor nodes, capable of communication with each other, as well as connectivity with backend, PCbased systems, thereby facilitating software development and data analysis in an integrated systems package. The core design principles of the sensor nodes enable operation in very mobile settings and truly ad-hoc, peer-to-peer interoperation without the intervention of a master or explicit middleware layer. The two main system properties highlighted in this paper are: 1) information distribution to all components within the system and 2) the usage of a common communication language in all system components. This language has been proprietarily developed for the Particle system and is known as ConCom. As a result of these system properties, we have found the Particle system to be very extensible and applicable in many everyday scenarios. The paper presents insights to the implementation of the Particle computer system, including software development and data analysis capabilities, and the overall system integration.

Distribution of media in the fast growing world of digital stored content and multimedia supporting devices with connectivity, calls for a new media distribution architecture. The user should be provided with the experience of having an overview of his full media collection, regardless of the time, the place, and the connectivity. The architecture presented in this paper, fulfils these needs and can cooperate furthermore with non-compliant devices.

In Ubiquitous computing small embedded sensor and computing nodes are one of the main enabling technologies. System programming for such small embedded systems is a challenging task involving various hardware components with different characteristics. This paper presents a file system for sensor nodes platforms providing a common organization structure and a lightweight and uniform access model for sensors and all other resources on sensor nodes. This mechanism forms an abstraction from different hardware, makes functions reuseable and simplifies the development on such systems. With ParticleFS an file system implementation on a sensor node platform is shown. As an example a telnet application running on sensor nodes was implemented demonstrating the usage of the approach for system programming on such platforms.

If a mobile computing device knows how it is positioned and oriented in relation to other devices nearby, then it can provide enhanced support for multi-device and multi-user interactions. Existing systems that provide position information to mobile computers are reliant on externally deployed infrastructure, such as beacons or sensors in the environment. We introduce the Relate system, which provides fine-grained relative position information to co-located devices on the basis of peer-to-peer sensing, thus overcoming dependence on any external infrastructure. The system is realised as a hardware/software plug-in, using ultrasound for peer-to-peer sensing, USB to interface with standard mobile devices, and data abstraction and inferencing to map sensor data to a spatial model that maintains both quantitative and qualitative relationships. We present a set of services and applications to demonstrate the utility of the system. We report experimental results on the accuracy of the relative position and orientation estimates, and other aspects of system performance.

We argue that among denial-of-service (DoS) attacks, link-layer jamming is a more attractive option to attackers than radio jamming is. By exploiting the semantics of the link-layer protocol (aka MAC protocol), an attacker can achieve better efficiency than blindly jamming the radio signals alone. We investigate some jamming attacks of S-MAC, what level of effectiveness and efficiency the attack can potentially achieve, and what countermeasures can be implemented against these attacks.

In this paper we present a novel TDMA-based medium access control (MAC) protocol for wireless sensor networks. Unlike conventional MAC protocols which function independently of the application, we introduce an Adaptive, Informationcentric and Lightweight MAC(AI-LMAC) protocol that adapts its operation depending on the requirements of the application. We also present a completely localised data management framework that helps capture information about traffic patterns in the network. This information is subsequently used by AI-LMAC to modify its operation accordingly. The data management framework can additionally be used for efficient query dissemination and query optimisation. We present preliminary results showing how the MAC protocol efficiently manages the issues of fairness and latency.

This article presents a cross-layered approach for networking in wireless sensor networks. WSNs differ greatly from traditional ad hoc wireless networks and therefore require the use of new types of network protocols that are energy-efficient to ensure a node lifetime of several years on a single battery and can operate without assistance of central managers in a dynamic network topology. We show that a tightly integrated set of networking protocols is a good solution to reach the target of highly energy-efficient WSNs. Our approach combines medium access organization with routing.

In this paper we address the localization problem for semistatic, randomly deployed, wireless sensor networks. The influence of the underlying random topology is taken in discussion and based on it we derive distance estimations function of the number of hops two nodes are separated by, and characterize the precision of these estimations. The results are applied to two well-known localization schemes (DVHop and DVDistance) and improvements of roughly 26 the first algorithm and 20 error are obtained. The introduced overhead is kept at a minimum as the resulting protocols are simpler than the original ones and only density information needs to be broadcasted to the nodes.

Guarding safety and security within industrial, commercial and military areas is an important issue nowadays. A specific challenge lies in the design of portable surveillance systems that can be rapidly deployed, installed and easily operated. Conventional surveillance systems typically employ stand alone sensors that transmit their data to a central control station for data-processing. One of the disadvantages of these kinds of systems is that they generate a lot of data that may induce processing or storage problems. Moreover, data from the sensors must be constantly observed and assessed by human operators. In this paper, a surveillance concept based on distributed intelligence in wireless sensor networks is proposed. In this concept, surveillance is automatically performed by means of many small sensing devices including cameras. The requirements for such surveillance systems are investigated. Experiments with a demonstration system were conducted to verify some of the claims made throughout this paper.

In this document we explore a TDMA based MAC protocol for WSNs. WSNs differ greatly from traditional ad hoc wireless networks like IEEE 802:11. This requires the usage of new types of MAC protocols, that are energy-efficient to ensure a node lifetime of several years on a single battery and can operate without assistance of base-stations. In the MAC protocol we present, nodes can autonomously choose a time slot, the transceiver usage is reduced to minimum, while nodes are provided with local topology information. The latter helps routing in the WSN and reduces routing messages. The MAC protocol also enables efficient transmission of short omni cast network maintenance messages, like routing and clustering messages.

In this paper we present a novel TDMA-based medium access control (MAC) protocol for wireless sensor networks. Unlike conventional MAC protocols which function independently of the application, we introduce an Adaptive, Information-centric and Lightweight MAC(AI-LMAC) protocol that adapts its operation depending on the requirements of the application. We also present a completely localised data management framework that helps capture information about traffic patterns in the network. This information is subsequently used by AI-LMAC to modify its operation accordingly. We present preliminary results showing how the MAC protocol efficiently manages the issues of fairness, latency and message buffer management.

DCOS is a Data Centric lightweight Operating System for embedded devices. Despite limited energy and hardware resources, it supports a data driven architecture with provisions for dynamic loadable Modules. It combines these with Real-Time provisions based on Earliest Deadline First with a simple but smart resource handling mechanism. We will give an overview of the capabilities of DCOS and we will describe the basics of the main mechanisms.

In this paper, we present two methods for calibration of acceleration sensors that are inexpensive, in-situ, require minimum user interaction and are targeted to a broad set of acceleration sensor applications and devices. We overcome the necessity of orthogonal axes alignment by extending existing calibration methods with a non-orthogonal axes model. Our non-orthogonal method can furthermore be used to enable automatic calibration for 1- or 2-axes accelerometers or realize a simultaneous mass-calibration of sensors with minimum effort. The influence of noise to the presented calibration methods is analysed.

In wireless sensor networks (WSN) the reliability of the system can be increased by providing several paths from the source node to the destination node and by sending the same packet through each of them (the algorithm is known as multipath routing). Using this technique, the traffic increases significantly. In this paper, we analyze the combination between a new multipath routing mechanism and a data-splitting scheme that results in an efficient solution for achieving high delivery ratios while keeping the traffic at a low value. Simulation results are presented in order to characterize the performances of the algorithm.

We present the architecture and design of a real time operating system for mobile wireless sensor networks. AmbientRT is being developed for environments with very limited resources in order to relieve the burden of the developer and to efficiently use the resources of the node. This paper presents the main concepts used and trade-offs involved in the system. Initial results show that with the current hardware available for sensor networks, the real time concept is feasible. For real-time scheduling we have designed EDFI. EDFI is a lightweight real-time scheduling protocol that combines EDF with deadline inheritance over shared resources. EDFI is precise with task admission control, very efficient with scheduling and dispatching, and straightforward in feasibility analysis.

Several factors were examined towards considering what influences users’ acceptability of alerting and informational messages in a field study conducted at ten homes. Through the simulation study message urgency was found to be a better predictor of acceptability than the degree of user engagement during ongoing activities. A model is proposed for including a range of additional factors expected to influence acceptability. The factors will be examined in forthcoming studies.

Ambient systems are networked embedded systems integrated with everyday environments and supporting people in their activities. These systems will create a Smart Surrounding for people to facilitate and enrich daily life and increase productivity at work. These systems will be quite different from current computer systems, as they will be based on an unbounded set of hardware artefacts and software entities, embedded in everyday objects or realized as new types of device. The ubiquitous computing vision has over the last 10 years inspired research into computing systems and applications that become pervasively embedded in our everyday environments, and that bring the unique flexibility of digital technology to the activities around which our lives evolve. Caused by rapid progress in technology, this early research tended to focus on experimental prototypes of infrastructure, devices, and applications. As the field is progressing, the most important research challenge and focus of this project is to develop the fundamental architecture of ubiquitous computing environments. Our approach to enable ambient systems depends on highly distributed, reliable, and secure information systems that can evolve and adapt to radical changes in their environment, delivering information services that adapt to the people and the services that use them. These distributed systems must easily and naturally integrate devices, ranging from tiny sensors and actuators to hand-held information appliances. Such devices will be connected primarily by short-range wireless networks, as well as by high-bandwidth local backbones.

Synchronous Distributed Jam Signalling (SDJS) is a new transmission scheme targeted to highly mobile and ad hoc wireless systems. It is based on the synchronous, parallel and superimposing emission of jam signal on the physical layer. SDJS is intended to be implemented as a feature on existing standards. It enables those system with the ability to fast estimate statistical parameters. This paper presents SDJS in general and then focuses on the application to estimate the parameter number of devices in a mobile setting. We studied SDJS and its application through a mathematical model and simulations and proved the idea in a realworld implementation on a mobile network, where we estimated the number of devices in real time (within 5ms), increasing the estimation speed compared to traditional approaches by factor 1000.

When we look at the developments within design over the last years, two major buzzwords emerge: interaction and experience. At the Faculty of Industrial Design Engineering we try to anticipate and respond to these directions in design tuning our assignments towards experience and interaction and by developing new design tools, techniques and even a new structure for our design courses. These tools, techniques and courses do not only aim at supporting and enhancing interaction and experience, they also aim at diversity. Because experiences are highly personal, we believe that diversity is one of the key-issues to be addressed [1]. The new structure, called the Boulevard of Inspiration, trains design students to take advantage of and expand their personal competencies, capitalise on their drive and passion and explore an abundant number of tools and techniques especially through the first phases of the design process in order to gain a rich variety of products, which fit the diversity of users. In this paper we will show a few of our achievements and discuss that designing for interaction and experience using the Boulevard of Inspiration and design techniques such as Tinkering and IA-Cards, seems a tempting, rewarding and feasible concept for contemporary design education.

Self organizing, wireless sensors networks are an emergent and challenging technology that is at- tracting large attention in the sensing and moni- toring community. Impressive progress has been done in recent years even if we need to assume that an optimal protocol for every kind of sensor net- work applications can not exist. As a result it is necessary to optimize the protocol for certain sce- narios. In many applications for instance latency is a crucial factor in addition to energy consumption. MERLIN performs its best in such WSNs where there is the need to reduce the latency while ensur- ing that energy consumption is kept to a minimum. By means of that, the low latency characteristic of MERLIN can be used as a trade o® to extend node lifetimes. The performance in terms of energy consumption and latency is optimized by acting on the slot length. MERLIN is designed speci¯cally to integrate routing, MAC and localization protocols together. Furthermore it can support data queries which is a typical application for WSNs. The MER- LIN protocol eliminates the necessity to have any explicit handshake mechanism among nodes. Fur- thermore, the reliability is improved using multiple path message propagation in combination with an overhearing mechanism. The protocol divides the network into subsets where nodes are grouped in time zones. As a result MERLIN also shows a good scalability by utilizing an appropriate scheduling mechanism in combination with a contention pe- riod.

In this paper, we present an energy-efficient medium access protocol designed for wireless sensor networks. Although the protocol uses TDMA to give nodes in the WSN the opportunity to communicate collision-free, the network is self-organizing in terms of time slot assignment and synchronization. The main goal of the medium access protocol is to minimize overhead of the physical layer. The protocol reduces the number of transceiver state switches and hence the energy wasted in preamble transmissions. The protocol is compared to SMAC and EMACs by simulation. The LMAC protocol is able to extend the network lifetime by a factor 2.4 and 3.8, compared to EMACs and SMAC respectively.

Wireless sensor networks (WSNs) are formed of tiny, highly energy-constrained sensor nodes that are equipped with wireless transceivers and can be used primarily in environmental monitoring applications. The nodes communicate with one another by autonomously creating ad-hoc multihop networks which are subsequently used to gather sensor data. WSNs also process the data within the network itself and only forward the result to the requesting node. This is referred to as in-network data aggregation and results in the substantial reduction of the amount of data that needs to be transmitted by any single node in the network. We present a framework for WSNs which would allow optimised query execution plans to be generated in a distributed manner within the network thus preventing the need to transmit network metadata all the way to a central server. Query plans also adapt continuously by monitoring varying network conditions to maintain energy-efficient operation thus maximising network lifetime.

This paper reports on work-in-progress of a cross-layered approach for networking in wireless sensor networks (WSNs) as currently being developed as part of the European research project EYES (IST- 2001-34734). Part of the overall goal of the EYES project is to develop new protocols and mechanism for WSNs, which are energy-ecient to ensure a node lifetime of several years on batteries, and which can operate without assistance of central managers in a dynamic network topology. The approach presented combines medium access organization, an im- plicit infrastructure creation, and routing. We show that a tightly inte- grated set of networking protocols is a viable solution to reach this target of highly energy-ecient WSNs. The medium access protocol consists of a fully distributed and self- organizing TDMA scheme, in which so called active nodes broadcast short control messages in their autonomously chosen time slot. At the same time, these short control messages are also used to create a con- nected subnetwork of these active nodes, while other, redundant nodes are passive and able to save energy by exploiting the so-created infras- tructure. The control message is also used by the routing protocol to establish and maintain ecient routes in a dynamic topology. The presented approach is compared to an existing communication solu- tion for WSNs, consisiting of SMAC for medium access control and DSR for the multi-hop routing of messages.

This paper presents EMACs, a medium access protocol especially designed for wireless sensor networks. The medium access protocol consists of a fully distributed and self-organizing TDMA scheme, in which each active node periodically listens to the channel and broadcasts a short control message. This control message is needed for medium access operation and is also used to piggy bag various types of information at low energy costs. Information in the control message is used to create a maximal independent set of nodes. This set of nodes creates a connected network and nodes in the set are active, while other nodes are passive and save energy by exploiting the infrastructure created by the connected network. The presented approach is compared in simulation with the SMAC protocol (a medium access protocol with coordinated adaptive sleeping) in a realistic multi-hop network setup where sensor reading are transported to a specific node and routes are established using the dynamic source routing protocol. The EMACs protocol is able to extend the network lifetime 30% to 55% compared to SMAC in a static network topology and in a dynamic network topology, EMACs prolongs the network lifetime with a factor 2.9 to 4.2.

In this paper we introduce a new distributed algorithm for location discovery. It can be used in wireless ad-hoc sensor networks that are equipped with means of measuring the distances between the nodes (like the intensity of the received signal strength). The algorithm takes the reliability of measurements into account during calculation of the nodes positions. Simulation results are presented, showing the algorithms performance in relation to its accuracy, communication and calculation costs. The simulation results of our approach yield 2 to 4 times better results in position accuracy than other systems described previously. This level of performance can be reached using only few broadcast messages with small and constant size, for each node in the network.