Pedro M. Wightman

A multiobjective approach to the relay placement problem in WSNs

This paper presents a multiobjective model for the simultaneous optimization of the number of relays and the energy dissipation when deploying a wireless sensor networks to monitor specific locations in an area. In order to solve the model, a hybrid evolutionary algorithm with two local searches is proposed an implemented. As the algorithm returns a set of efficient solutions, the tradeoff among placements in their number of relays with their energy dissipation is explored. The evaluation shows that the energy can be diminished greatly by choosing not the most efficient placement in terms of number of relays but other placement with more relays. In our experiments, it was found that the solution with one or two more relay sensors than the efficient placement helped greatly in diminishing the energy. The proposed algorithm also showed better approximations than an approximation problem in the literature to the minimal number of relays.

A family of simple distributed minimum connected dominating set-based topology construction algorithms

This paper considers the problem of topology construction to save energy in wireless sensor networks. The proposed topology construction mechanisms build reduced topologies using the Connected Dominating Set approach in a distributed, efficient, and simple manner. This problem is very challenging because the solution must provide a connected network with complete coverage of the area of interest using the minimum number of nodes possible. Further, the algorithms need to be computationally inexpensive and the protocols simple enough in terms of their message and computation complexity, so they do not consume more energy creating the reduced topology than the energy that they are supposed to save. In addition, it is desirable to reduce or completely eliminate the need of localization mechanisms since they introduce additional costs and energy consumption. To this end, we present the family of A3 distributed topology construction algorithms, four simple algorithms that build reduced topologies with very low computational and message complexity without the need of localization information: A3, A3Cov, A3Lite and A3CovLite. The algorithms are compared in sparse and dense networks versus optimal theoretical bounds for connected-coverage topologies and two distributed heuristics found in the literature using the number of active nodes and the ratio of coverage as the main performance metrics. The results demonstrate that there is no clear winner, and rather, trade offs exist. If coverage is not as critical as energy (network lifetime), it would be better to use A3Lite, as it needs fewer number of nodes and messages. If coverage is very important for the application, then the A3CovLite is the best option mostly because of the lower message complexity.

A3Cov: A new topology construction protocol for connected area coverage in WSN

Topology control is a well-known strategy to save energy and extend the lifetime of wireless sensor networks. It consists of topology construction and topology maintenance algorithms. While topology construction builds a reduced topology, topology maintenance changes the reduced topology when the current one is no longer optimal. The selection of an appropriate topology maintenance technique is rarely included in the evaluation of topology control solutions, even though the impact of such decision in the lifetime of the network (in terms of number of nodes or coverage) has been shown before. This paper makes two important contributions. First, it introduces a new topology construction algorithm called A3Cov, based on the A3 protocol, which increases the coverage ratio considerably compared to the original version. Second, the A3Cov protocol is evaluated jointly with four topology maintenance techniques to determine the influence of the different maintenance schemes on the area coverage and the network lifetime. The results show that the dynamic global topology maintenance techniques with A3Cov provide the best coverage and network lifetime for a substantially longer period of time compared to the ACOS protocol.

Information and communication technologies and climate change adaptation in Latin America and the Caribbean: a framework for action

Despite ongoing interest in deploying information and communication technologies (ICTs) for sustainable development, their use in climate change adaptation remains understudied. Based on the integration of adaptation theory and the existing literature on the use of ICTs in development, we present an analytical model for conceptualizing the contribution of existing ICTs to adaptation, and a framework for evaluating ICT success. We apply the framework to four case studies of ICTs in use for early warning systems and managing extreme events in the Latin American and the Caribbean countries. We propose that existing ICTs can support adaptation through enabling access to critical information for decision-making, coordinating actors and building social capital. ICTs also allow actors to communicate and disseminate their decision experience, thus enhancing opportunities for collective learning and continual improvements in adaptation processes. In this way, ICTs can both communicate the current and potential impacts of climate change, as well as engage populations in the development of viable adaptation strategies.

High variability geographical obfuscation for location privacy

In the last few years, the number of applications that use the location of the users in order to provide a more personalized service have been increasing, mainly due to easy access to low cost smartphones, geographical positioning systems and other factors, like social networking. The concern of protecting this information is also increasing due to the capabilities than an eventual attacker could have if the location information is obtained. Some protection techniques have been proposed in the literature; for example, location obfuscation which slightly alters the location to hide the real one. However, this technique could be filtered out with time series-based mechanisms. In this work, the Pinwheel obfuscation technique is proposed in order to reduce the possibility of EMA-based filtering based on high variability and asymmetry of the induced noise. The results show that the level of filtered noise is reduced from 35% in N-RAND and 30% in θ-Rand obfuscation techniques, to 15% in Pinwheel, with asymmetric scenarios, while preserving a long final average distance from the original path after a filtering attack.

An optimal solution to the MCDS problem for topology construction in wireless sensor networks

Topology Construction (TC) is a very well-known technique to save energy and extend the lifetime of wireless sensor networks. One common approach to implement TC is to select a small subset of nodes that can accomplish the global objective of the network and put the rest of the nodes in a low energy consumption mode to use their energy in the future. One way to select this subset of nodes is by solving the Minimum Connected Dominating Set problem (MCDS). This paper presents a Mixed Integer Programming (MIP) formulation that finds the optimal solution to this problem. The formulation is proposed as a benchmarking tool to compare the performance of existing and new heuristics that approximate the solution to the same problem. In fact, the paper compares the performance of three well-known CDS-based topology construction protocols versus the MIP-MCDS formulation. The results show that, in terms of the size of the CDS, the distance between the optimal and the approximate solutions increases with the communication radius and the number of nodes. In terms of the solution time, for low density and high node degree topologies the mathematical programming formulation is comparable, and sometimes better, to that of the heuristics. However, in topologies with low node degree and high node density the heuristic solutions outperform the mathematical programming solution.

LatinCon16 - Topology Maintenance: Extending the Lifetime of Wireless Sensor Networks

Topology Maintenance is the part of Topology Control dedicated to the periodical restoration of the network topology, in order to guarantee characteristics like connectivity and coverage. This article presents one of the first efforts to formalize this concept by presenting a taxonomy for different strategies to perform topology maintenance in wireless sensor networks, including static, dynamic and hybrid techniques, with global and local scope, and using different triggering criteria. In addition, a comparison is included to evaluate, in sparse and dense networks, the performance of global static, dynamic and hybrid techniques, with triggering criteria based on time and energy, and working jointly with the two well-known topology construction protocols A3 and CDS-Rule-K. The results show that the dynamic techniques always produce benefits in terms of extending the network lifetime, while static and hybrid techniques produce mixed results (worst and best), depending mainly on the nature of the construction protocols used.

Near-Rand: Noise-based location obfuscation based on random neighboring points

In recent years Location-Based Information Systems have increased its popularity in the market of mobile applications, however, due to the ability of smartphones and similar devices to estimate location in real time using GPS or through network providers; it is critical to implement techniques to protect such sensitive information while still make it available to the service provider. This paper presents Near-Rand, a new random noise-based location obfuscation technique. This algorithm generates random points around the real location of the user within a neighbor-size squared area and calculates the n nearest points average to the users location giving as result an obfuscated point. Compared to Pinwheel, another noise-based obfuscation mechanism, it shows a similar performance against Exponentially Moving Average-based filtering attacks, while being able to use non-uniformly distributions for random points.

Empirical approach to network sizing for connectivity in wireless sensor networks with realistic radio propagation models

Choosing the appropriate network size to guarantee connectivity in a WSN deployment is a challenging and important question. Classic techniques to answer this question are not up to the challenge because they rarely consider realistic radio models. This work proposes a methodology to evaluate the performance of network size estimation techniques in terms of connectivity efficiency under realistic radio scenarios. This study is carried out using Atarraya, a simulation tool for wireless sensor networks, considering three classical estimation techniques and a radio model based on the specifications of the ZigBee radio from off-the-shelf WaspMote nodes from Libelium. The results show that the hexagon-based optimal grid technique provides the most efficient estimate, offering a high connectivity level with the lowest estimated number of nodes for a given proximity radius parameter, followed by the circle packing and the triangle-based grid distribution. In addition, the results show that packet error rates of 10% could still produce highly connected topologies.

An Initial Evaluation of the Impact of Location Obfuscation Mechanisms on Geospatial Analysis

Since the emergence of GPS capable mobile devices and the increasing demand of contextual services such as location-based services (LBSs), there has been a rising concern for location privacy. This led to the creation of manifold location privacy protection mechanisms (LPPMs) in the scientific community. The authors propose the use of geospatial analyses as an evaluation tool of the impact of noise-based algorithms on location data. For this, the Pinwheel mechanism is tested, using different noise settings, to identify a threshold where privacy is provided, and geostatistical inferences are not affected greatly. Results show that 500 m of random noise introduce a small level of change that does not change the general trend in both heatmap and hotspot analysis but still can provide a minimum level of protection to individuals.