A large class of Wireless Sensor Networks (WSN) applications involve a set of isolated urban areas (e.g., urban parks or building blocks) covered by sensor nodes (SNs) monitoring environmental parameters. Mobile sinks (MSs) mounted upon urban vehicles with fixed trajectories (e.g., buses) provide the ideal infrastructure to effectively retrieve sensory data from such isolated WSN fields. Existing approaches involve either single-hop transfer of data from SNs that lie within the MS's range or heavy involvement of network periphery nodes in data retrieval, processing, buffering, and delivering tasks. These nodes run the risk of rapid energy exhaustion resulting in loss of network connectivity and decreased network lifetime. Our proposed protocol aims at minimizing the overall network overhead and energy expenditure associated with the multihop data retrieval process while also ensuring balanced energy consumption among SNs and prolonged network lifetime. This is achieved through building cluster structures consisted of member nodes that route their measured data to their assigned cluster head (CH). CHs perform data filtering upon raw data exploiting potential spatial-temporal data redundancy and forward the filtered information to appropriate end nodes with sufficient residual energy, located in proximity to the MS's trajectory. Simulation results confirm the effectiveness of our approach against as well as its performance gain over alternative methods.

Mobile tourist guides have been in the spotlight during the past decade resulting in many prototypes, either full-fledged standalone mobile applications or web-based applications. Particular emphasis has been given to personalisation of services, typically based on travel recommender systems used to assist tourists in choosing places to visit; these systems address an important aspect of personalization and hence reduce the information burden for the user. However, existing systems fail to exploit information, behaviors, ideas, evaluations, assessments, ratings, etc, by other tourists with similar interests, which provide ground for the cooperative production of tourist content and travel recommendations. In this paper we extend this notion of travel recommender systems utilizing collaborative filtering techniques for deriving improved recommendations. We also propose the use of Wireless Sensor Network (WSN) installations around tourist sites for providing mobile users convenient and inexpensive means for uploading tourist information and ratings about Points of Interest (POI) via their mobile devices. User ratings uploaded through WSN infrastructures are weighted higher to differentiate between users that rate POIs using the mobile tourist guide application in direct proximity of the POI and others using the Internet away from the POI.

A key feature of wireless sensor networks (WSNs) is the collaborative processing, where the correlation existing over the local data of sensor nodes (SNs) is exploited so that the total data volume can be reduced (data aggregation). The use of Mobile Agents (MAs), i.e., software entities able of migrating among nodes and resuming execution naturally, fits in this scenario; the local data of an SN can be combined with the data collected by an MA from other SNs in a way that depends on the specific program code of the MA. In this paper, we consider the problem of calculating near-optimal routes for MAs that incrementally aggregate the data as they visit the nodes in a distributed sensor network. Our algorithm follows a greedy-like approach always selecting the next node to be included in an itinerary in such a way that the cost of the so far formed itineraries is kept minimum at each step. Simulation results confirm the high effectiveness of the proposed algorithm as well as its performance gain over alternative approaches. Also, with the use of proper data structures, the computational complexity of the algorithm is kept low as it is formally proved in the paper.

Abstract Jamming is defined as the act of intentionally directing electromagnetic energy towards a communication system to disrupt or prevent signal transmission. In the context of wireless sensor networks (WSNs), jamming is the type of attack which interferes with the radio frequencies used by sensor nodes and may be viewed as a special case of denial of service (DoS) attacks. Herein, we outline the possible jamming attacks a WSN may encounter. The main contribution of this paper is the outline of the design specifications of a prototype node ‘Ares’ that effectively defends jamming attacks. Our focus is on frequency hopping spread spectrum (FHSS) and direct sequence spread spectrum (DSSS), two of the most effective countermeasures against jamming. The main novel aspect of Ares is that it uses a hybrid FHSS–DSSS approach to defend jamming attacks. We suggest the use of a specific FHSS technique in 5 GHz band with 51 frequency channels wherein the channel sequence is generated using a key (which derives from a secret word), known only to the sink and the sensor nodes, as a seed. Each channel uses DSSS modulation with 16‐bit pseudo noise (PN) code. The PN code derives from the same key used for FHSS channel generation. The pre‐eminence of our method against alternative anti‐jamming techniques is demonstrated through extensive simulation tests. Copyright © 2008 John Wiley & Sons, Ltd.

Mobile agents (MAs) have been initially developed to replace the client/server model which shows many disadvantages in WSN environments (e.g. very high bandwidth and energy utilization). Herein, we present CBID (Clone-Based Itinerary Design), a novel algorithm that calculates near-optimal routes for MAs that incrementally fuse the data as they visit the nodes while enabling a fast update of designed itineraries which is especially important for highly dynamic topologies. The order of visited nodes highly affects the quality and the overall cost of data fusion. The key MAs characteristic exploited by CBID to reduce energy consumption and response time is their cloning capability. Parallel dispatched MAs sequentially visit sensor nodes arranged in tree structures and upon visiting a node with two or more child nodes, the MAs (master MAs) clone of themselves with each clone (slave MA) visiting a tree branch. When all slave MAs return to that node, report their data to the master MA and are self-destroyed. This results in highly reduced energy consumption and response time since many MAs work in parallel. Simulation results prove the high effectiveness of CBID in data fusion tasks compared to other alternative algorithms.

In this article, we consider the problem of calculating an appropriate number of near-optimal (subject to a certain routing objective) routes for mobile agents (MAs) that incrementally fuse the data as they visit the nodes in a distributed sensor network. We propose an improved heuristic algorithm which computes an approximate solution to the problem by suggesting an appropriate number of MAs and constructing near-optimal itineraries for each of them. The performance gain of our algorithm over alternative approaches both in terms of cost and task completion latency is demonstrated by a quantitative evaluation and also in simulated environments through a Java-based tool.

Wireless sensor networks (WSNs) are used in many applications which often include the monitoring and recording of sensitive information. Hence, their critical importance raises many security concerns. In the context of WSNs, jamming is the type of attack which interferes with the radio frequencies used by network nodes. In the event that an attacker uses a rather powerful jamming source, disruptions of WSNs proper function are likely to occur. As a result, the use of countermeasures against jamming in WSN environments is of immense importance. The main contribution of this article is the discussion of various defence methods against jamming that would allow a WSN to survive and work properly in a hostile jamming environment. Our focus is on frequency hopping spread spectrum (FHSS) and direct sequence spread spectrum (DSSS), two of the most effective countermeasures against jamming. We suggest the use of a specific FHSS technique in 5 GHz band with 55 frequency channels wherein the channel sequence is generated using a secret word, known only to the sink and the sensor nodes, as a seed. Each channel uses DSSS modulation with 16 bit Pseudo Noise (PN) code, which derives from the same secret word used for FHSS channel generation.