Wireless Sensor and Actor Networks

In wireless sensor and actor network research, the commonly used mobility models for a mobile actor are random walk model, random waypoint mobility model, or variants thereof. For a fully connected network, the choice of mobility model for the actor is not critical because, there is at least one assured path from the sensor nodes to the actor node. But, for a sparsely connected network where information cannot propagate beyond a cluster, random movement of the actor may not be the best choice to maximize event detection and subsequent action. This paper presents encouraging preliminary results with static intelligent mobility models that are found using the inherent clusters’ information of a sparsely connected network. Finally, a proposal to develop dynamic intelligent mobility models for the actor based on a mathematical model is presented.

In the last few years, WSN has been object of an intense research activity that has determined an important improvement by technologic and computation point of view both. The notable level got and the increasing request of applications designed over Sensor Networks make WSN commercial diffusion next to be a fact. Limited resource orientation and high level application requirements result in a number of key open issues, such as Resource Optimization and Quality of Service. These last two issues require an important preliminary phase of analysis and evaluation that can provide the designer with knowledge of important relationships between parameters design and application desired characteristics. Mathematical models of local resource (node), of network influence on single resource, of QoS requests, and related analysis techniques to determine not only “how much” but also “in which way” resources are expensed are proposed in this paper.

Wireless Sensor and Actor Networks (WSAN) constitute a growing research field in several engineering areas. One very interesting domain of WSAN application is precision agriculture, and in particular, the automatic control of tree irrigation depending on sap flow levels. Nowadays, the software development process followed in these kinds of applications is largely dependent on the platform where the final implementation is done. Consequently, commonly desired attributes such as flexibility, reuse and evolution are relegated to a second level of priority. Nevertheless, the growing interest in WSAN has been led to advances from different points of view: new application domains, new middleware, new simulation environments, and so on. In spite of all these advances, WSAN development is today needed of concrete mechanisms that make easy the software generation process. This paper summarizes our contribution in this field from two points of view: as an agronomic solution and as new opportunities for affording the construction of these systems taking into consideration the most recent advances in software engineering.¹

Placing fire detectors in a forest is usually associated with powering problems since the sensors do not have access to external power supply and a periodical change of internal batteries is an undesired option. This paper presents an approach where the fire sensor itself, when heated by nearby fire, generates electrical energy to power a radio transmitter. Presented energizing fire sensor is environmentally friendly and can be mass produced at a very low cost. Upon activation the sensor produces enough power necessary to operate most standard radio transmitters depending on what communication system is chosen for operation. The fire detector unit can be deployed from either helicopter or manually from the ground. The sensor can be designed to activate itself at different temperatures to suit different climate zones. Rough guidelines are given for estimation of attenuation of radio wave propagation in forest areas in order to predict maximum transmit distance.

In this paper, the design and implementation of a wireless communication system specific to wide area sensor network capable of establishing ad hoc connections is presented. First, the application to which this system is applied is explained, and then a brief description of the system is made. In this system two routing algorithms were implemented, one based on a static links routing table and the other is the M to 1 algorithm proposed by Lou W. in [1]. Tests were carried out with the designed system and the routing algorithms mentioned, accomplishing satisfactory communication between nodes in a test scenario for the first case.

In this paper, a routing protocol is proposed that provides location privacy for the source and the destination as well as user anonymity and unlinkability in multihop wireless sensor networks. The sink is assumed to be computationally powerful and responsible for all routing decisions. It assigns incoming and outgoing labels to nodes in the uplink and downlink directions. Each node is only aware of its own labels and only forwards packets whose labels match either its downlink or uplink incoming label. Moreover, in order to prevent packet tracing by a global eavesdropper, layered cryptography is used in both directions to make a packet look randomly different on different links. However, due to the node capability limitations, only symmetric cryptography is used.

In this paper, a formal analysis of security protocols in the field of wireless sensor networks is presented. Two complementary protocols, TinySec and LEAP, are modelled using the high-level formal language HLPSL, and verified using the model checking tool Avispa, where two main security properties are checked: authenticity and confidentiality of messages. As a result of this analysis, two attacks have been found: a man-in-the-middle- attack and a type flaw attack. In both cases confidentiality is compromised and an intruder may obtain confidential data from a node in the network. Two solutions to these attacks are proposed in the paper.

The development and deployment of robust and highly populated Wireless Sensor Networks require addressing a wide variety of challenges. Among them, the synchronization and energy management of the nodes composing the network have been identified as two challenges to overcome. In this paper, we follow a cross-layer approach by defining a synchronous engine built across the radio, MAC and routing layers. The design of our proposal has been based on the results of our previous research efforts dealing with various experimental platforms and experimental trials.

Ad hoc routing technology has been developed primarily for networks of mobile nodes. The operational life of untethered nodes will be limited by its power source, so ad hoc networks strongly depend on the efficient use of their batteries. All the layers of communication are coupled in power consumption and solutions addressing the power saving issue include transmission power control, power aware routing and low power modes at the physical layer. At the network layer, routing protocols may balance power consumption at nodes according to their routing decisions. Several authors have proposed power aware routing algorithms based on power cost functions. In this work we present a performance comparison of the DSR (Dynamic Source Routing) and the OLSR (Optimized Link State Routing) in terms of energy consumption. We evaluate how the different approaches affect the energy usage of mobile devices. We found that a reactive protocol takes advantage of its routing policy when the traffic load is low. However, at higher traffic rates, a proactive routing protocol can perform better with an appropriate refresh parameter. In addition, we showed how, independently from the routing protocol selected, the overhearing activity can seriously affect the performance since all the neighbours of a transmitting node also consume their energy. To the best of our knowledge, this is the first simulation study addressing the power saving issue to extensively compare the DSR and OLSR protocols under a wide variety of network scenarios.

In this paper, we study the applicability of an emerging RFID-based communication technology, NFC (Near Field Communication), to ultra-low power wireless sensors. We present potential application examples of passive and semi-passive NFC-enabled sensors. We compare their NFC-based implementations to corresponding implementations based on short-range radios such as Bluetooth and Wibree. The comparison addresses both technical properties and usability. We also introduce Smart NFC Interface, which is our general-purpose prototype platform for rapid prototyping of NFC and Bluetooth implementations. Two pilot sensor implementations and an NFC-Bluetooth gateway implementation based on our platform are presented and evaluated. Finally, needs and possibilities for technical improvements of available NFC technology are discussed.

A wireless sensor network (WSN) is a wireless network composed of spatially distributed and tiny autonomous nodes — smart dust sensors, motes —, which cooperatively monitor physical or environmental conditions. Nowadays these kinds of networks support a wide range of applications, such as target tracking, security, environmental control, habitat monitoring, source detection, source localization, vehicular and traffic monitoring, health monitoring, building and industrial monitoring, etc. Generally, these applications have strong and strict requirements for end-to-end delaying and loosing during data transmissions. In this paper, we propose a realistic scenario for application of the WSN field in order to illustrate selection of an appropriate approach for guaranteeing performance in a WSN-deployed application. The methodology we have used includes four major phases: 1) Requirements analysis of the application scenario; 2) QoS modeling in different layers of the communications protocol stack and selection of more suitable QoS protocols and mechanisms; 3) Definition of a simulation model based on an application scenario, to which we applied the protocols and mechanisms selected in the phase 2; and 4) Validation of decisions by means of simulation and analysis of results. This work has been partially financed by the “Universidad Politécnica de Madrid” and the “ Comunidad de Madrid” in the framework of the project CRISAL - M0700204174.

Device localization or positioning is a key issue in wireless sensor networks applications. One solution widely used to estimate the position of a node in the network consists in using the intersection of coverage areas. For the sake of simplicity, these areas have traditionally been modeled by rectangles, assuming some extra inaccuracy. In this paper we propose a localization algorithm based on hexagonal intersection. Results show that the only substitution of the geometric shape provides better results in the localization of the devices composing the network.

Popularity of ubiquitous computing increases the importance of location-aware applications, which increases the need for finding location of the user. In this paper, we present a novel localization method for indoor environments using Wi-Fi infrastructure.

While localization using Wi-Fi is cost effective, handling the obstructions which are the main cause of signal propagation error in indoor environments is a challenging task. We address this problem in two levels, resulting in increased accuracy of localization. In the first level, we “localize” the residing area of user node in coarse granularity. Then, we use building layout to find the objects that attenuate the signal between the reference node and the coarse estimate of the location of user node. Using multi-wall propagation model, we apply corrections for all obstructions and find the location of user node. Empirical results based on experiments conducted in lab-scale, shows meter-level accuracy.

Approximate information on the location of nodes in a sensor network is essential to many types of sensor network applications and algorithms. In many cases, using symbolic coordinates is an attractive alternative to the use of geographic coordinates due to lower costs and lower requirements on the available location information during coordinate assignment. In this paper, we investigate different possible methods of assigning symbolic coordinates to sensor nodes. We present a method based on broadcasting coordinate messaging and filtering using sensor events. We show in the evaluation that this method allows a reliable assignment of symbolic coordinates while only generating a low overhead.

This paper evaluates three routing strategies for wireless sensor networks: source, shortest path, and hierarchical-geographical, which are the three most commonly employed by wireless ad-hoc and sensor networks algorithms. Source routing was selected because it does not require costly topology maintenance, while shortest path routing was chosen because of its simple discovery routing approach and hierarchical-geographical routing was elected because it uses location information via Global Positioning System (GPS). The performance of these three routing strategies is evaluated by simulation using OPNET, in terms of latency, End to End Delay (EED), packet delivery ratio, routing overhead, overhead and routing load.

Geographic routing is a well established solution for scalingin large wireless ad-hoc networks. A fundamental issue is forwarding packets around voids to reach destinations in networks with sparse topologies. All general known solutions need first to get into a dead end, at link level, to be able afterwards to apply a recovery algorithm. These techniques can lead to very inefficient forwarding paths. We propose a novel general approach, based on light weight connectivity maps, C-Maps, distributed among all the nodes in the network to obtain more efficient and robust paths. The main contribution of our method is the distributed Mercator protocol that builds these maps. Each node in this protocol builds and maintains its own C-Map that summarizes connectivity information of all the network around itself using hierarchical regions. This information is more precise from regions closer to the node. Nodes apply greedy forwarding and face routing to the different hierarchical levels of connectivity information. Better paths are obtained with this behavior. Robustness is guaranteed by every node containing its CMap. Our analytical and simulation work shows that the map state and the communication overhead grows logarithmically with the size of the network.

We present a hardware/software implementation of the IEEE 802.15.3 MAC protocol. Processing-intensive and time-critical protocol tasks are handled by a protocol accelerator that is integrated on-chip with a 32-bit general-purpose processor in order to achieve a moderate (20-40 MHz) system clock frequency. This enables low-power wireless devices compliant with this standard, providing high data rate, multimedia communication.

One of the main tasks of the protocol accelerator is to analyze received or transmitted beacons. Based on the channel time allocations broadcast in the beacon and frame information stored in a hardware transmission queue, frames are transmitted without immediate control of the processor. Other features of the protocol accelerator include CRC generation, handling of immediate acknowledgment frames, and direct memory access.

WSNs are becoming an important topic in the research arena. Their low cost and the wide range of applications where wireless sensor networks can be applied, make them an important research and commercial field in the short term. Furthermore, the IEEE 802.15.4 standard for physical and MAC layer in addition with the Zigbee specification for the network and application layer, are an enforcement for WSNs. Much research in WSNs related topics such as energy-aware, MAC protocols, routing protocols, security, location, etc is being carried out nowadays. An open issue is the interconnection between wireless sensor networks where different approaches can be adopted: bridging (extension devices) and proxying (mainly middleware entities). This paper is focused in the bridging approach for Zigbee networks. Our objective is to establish a Zigbee Extension Device Network for the case where the different clusters can not be connected to the same Zigbee network by using the multihop routing protocol defined in Zigbee. A Zigbee cluster is a set of Zigbee nodes. This paper introduces three different solutions to join the disconnected clusters of the Zigbee Network: a central approach (based on the use of a central station) and two distributed approaches; one of them proposes that each Zigbee Extension Device stores the information of all the other Extension Devices within the network while the other uses a P2P Zigbee Extension Device Overlay Network to join the disconnected Zigbee Clusters. The paper includes the analysis of each solution and the comparison among them.