541 research outputs found
A Topology Reorganization Scheme for Reliable Communication in Underwater Wireless Sensor Networks Affected by Shadow Zones
Effective solutions should be devised to handle the effects of shadow zones in Underwater Wireless Sensor Networks (UWSNs). An adaptive topology reorganization scheme that maintains connectivity in multi-hop UWSNs affected by shadow zones has been developed in the context of two Spanish-funded research projects. A mathematical model has been proposed to find the optimal location for sensors with two objectives: the minimization of the transmission loss and the maintenance of network connectivity. The theoretical analysis and the numerical evaluations reveal that our scheme reduces the transmission loss under all propagation phenomena scenarios for all water depths in UWSNs and improves the signal-to-noise ratio
Dynamic Vehicle Routing for Data Gathering in Wireless Networks
We consider a dynamic vehicle routing problem in wireless networks where
messages arriving randomly in time and space are collected by a mobile receiver
(vehicle or a collector). The collector is responsible for receiving these
messages via wireless communication by dynamically adjusting its position in
the network. Our goal is to utilize a combination of wireless transmission and
controlled mobility to improve the delay performance in such networks. We show
that the necessary and sufficient condition for the stability of such a system
(in the bounded average number of messages sense) is given by {\rho}<1 where
{\rho} is the average system load. We derive fundamental lower bounds for the
delay in the system and develop policies that are stable for all loads {\rho}<1
and that have asymptotically optimal delay scaling. Furthermore, we extend our
analysis to the case of multiple collectors in the network. We show that the
combination of mobility and wireless transmission results in a delay scaling of
{\Theta}(1/(1- {\rho})) with the system load {\rho} that is a factor of
{\Theta}(1/(1- {\rho})) smaller than the delay scaling in the corresponding
system where the collector visits each message location.Comment: 19 pages, 7 figure
EFFICIENT DYNAMIC ADDRESSING BASED ROUTING FOR UNDERWATER WIRELESS SENSOR NETWORKS
This thesis presents a study about the problem of data gathering in the inhospitable
underwater environment. Besides long propagation delays and high error probability,
continuous node movement also makes it difficult to manage the routing information
during the process of data forwarding. In order to overcome the problem of large
propagation delays and unreliable link quality, many algorithms have been proposed
and some of them provide good solutions for these issues, yet continuous node
movements still need attention. Considering the node mobility as a challenging task,
a distributed routing scheme called Hop-by-Hop Dynamic Addressing Based (H2-
DAB) routing protocol is proposed where every node in the network will be assigned
a routable address quickly and efficiently without any explicit configuration or any
dimensional location information. According to our best knowledge, H2-DAB is first
addressing based routing approach for underwater wireless sensor networks
(UWSNs) and not only has it helped to choose the routing path faster but also
efficiently enables a recovery procedure in case of smooth forwarding failure. The
proposed scheme provides an option where nodes is able to communicate without
any centralized infrastructure, and a mechanism furthermore is available where
nodes can come and leave the network without having any serious effect on the rest
of the network. Moreover, another serious issue in UWSNs is that acoustic links are
subject to high transmission power with high channel impairments that result in
higher error rates and temporary path losses, which accordingly restrict the
efficiency of these networks. The limited resources have made it difficult to design a
protocol which is capable of maximizing the reliability of these networks. For this
purpose, a Two-Hop Acknowledgement (2H-ACK) reliability model where two
copies of the same data packet are maintained in the network without extra burden
on the available resources is proposed. Simulation results show that H2-DAB can
easily manage during the quick routing changes where node movements are very
frequent yet it requires little or no overhead to efficiently complete its tasks
Machine Learning in Wireless Sensor Networks: Algorithms, Strategies, and Applications
Wireless sensor networks monitor dynamic environments that change rapidly
over time. This dynamic behavior is either caused by external factors or
initiated by the system designers themselves. To adapt to such conditions,
sensor networks often adopt machine learning techniques to eliminate the need
for unnecessary redesign. Machine learning also inspires many practical
solutions that maximize resource utilization and prolong the lifespan of the
network. In this paper, we present an extensive literature review over the
period 2002-2013 of machine learning methods that were used to address common
issues in wireless sensor networks (WSNs). The advantages and disadvantages of
each proposed algorithm are evaluated against the corresponding problem. We
also provide a comparative guide to aid WSN designers in developing suitable
machine learning solutions for their specific application challenges.Comment: Accepted for publication in IEEE Communications Surveys and Tutorial
Design of Three-Tiered Sensor Networks with a Mobile Data Collector under Energy and Buffer Constraints
A sensor network consists of a network with a large number of sensor nodes deployed around some phenomenon to gather information. Since the nature of sensor nodes is that their energy is limited, many techniques focus on addressing the problem of minimizing the energy consumption in order to extend the network lifetime. One approach is to deploy relay nodes. However, the requirement to transmit over large distances leads to a high rate of energy dissipation. Therefore, mobile data collectors are introduced to resolve this problem. In this thesis, we present an Integer Linear Programming formulation that takes different parameters into consideration to determine an optimal relay node placement scheme in networks with a mobile data collector, which ensures that there is no data loss and the energy dissipation does not exceed a specified level. The simulation results show that our formulation can significantly extend the network lifetime and provide Quality of Service
Controlled mobility in stochastic and dynamic wireless networks
We consider the use of controlled mobility in wireless networks where messages arriving randomly in time and space are collected by mobile receivers (collectors). The collectors are responsible for receiving these messages via wireless transmission by dynamically adjusting their position in the network. Our goal is to utilize a combination of wireless transmission and controlled mobility to improve the throughput and delay performance in such networks. First, we consider a system with a single collector. We show that the necessary and sufficient stability condition for such a system is given by ρ<1 where ρ is the expected system load. We derive lower bounds for the expected message waiting time in the system and develop policies that are stable for all loads ρ<1 and have asymptotically optimal delay scaling. We show that the combination of mobility and wireless transmission results in a delay scaling of Θ([1 over 1−ρ]) with the system load ρ, in contrast to the Θ([1 over (1−ρ)[superscript 2]]) delay scaling in the corresponding system without wireless transmission, where the collector visits each message location. Next, we consider the system with multiple collectors. In the case where simultaneous transmissions to different collectors do not interfere with each other, we show that both the stability condition and the delay scaling extend from the single collector case. In the case where simultaneous transmissions to different collectors interfere with each other, we characterize the stability region of the system and show that a frame-based version of the well-known Max-Weight policy stabilizes the system asymptotically in the frame length.National Science Foundation (U.S.) (Grant CNS-0915988)United States. Army Research Office. Multidisciplinary University Research Initiative (Grant W911NF-08-1-0238
Index to 1981 NASA Tech Briefs, volume 6, numbers 1-4
Short announcements of new technology derived from the R&D activities of NASA are presented. These briefs emphasize information considered likely to be transferrable across industrial, regional, or disciplinary lines and are issued to encourage commercial application. This index for 1981 Tech Briefs contains abstracts and four indexes: subject, personal author, originating center, and Tech Brief Number. The following areas are covered: electronic components and circuits, electronic systems, physical sciences, materials, life sciences, mechanics, machinery, fabrication technology, and mathematics and information sciences
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