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Distributed subspace projection over Wireless Sensor Networks with unreliable links Distributed subspace projection over Wireless Sensor Networks with unreliable links

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Date added: 12/30/2013
Date modified: 12/30/2013
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The inaccuracy of the measurements collected by sensor nodes in a Wireless Sensor Network motivates the use of appropriate techniques for reducing this observation error. One of the most widely used method consists of projecting orthogonally the observation signal onto a subspace of interest. The in-network processing nature of these architectures suggests that such a method should be performed in a distributed manner, through successive local communications between neighbors and under a time-varying network topology. Existing approaches to this technique assume an ideal scenario, where these communications are not subject to interferences, packet losses or fading. In this work, we propose a new technique, which under unreliable communications, projects the initial observation onto a proper subspace in a totally distributed fashion. We analyze the deviation from the optimal projection due to packet losses, and compare it with the initial observation error. We also consider the additional error due to an inaccurate choice of the subspace. Simulation results are presented to show the efficiency and validity of our approach.

Dynamic Inhibition Areas for Accurately Solving the Shortest Link Scheduling Problem Dynamic Inhibition Areas for Accurately Solving the Shortest Link Scheduling Problem

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Date added: 12/30/2013
Date modified: 12/30/2013
Filesize: 286 Bytes
Downloads: 1220

We present a novel distributed algorithm, called Dynamic Inhibition Area Link Scheduling (DIA-LS), which efficiently solves the Shortest Link Schedule (SLS) problem in wireless ad-hoc networks. The schedule length is reduced by maximizing the spatial reusability, which is the number of simultaneous transmissions per unit area, obtaining a dense feasible transmission pattern at each time slot. Most algorithms in the literature assume binary or protocol interference models and are based on uniformly partitioning the network deployment area. It leads to inaccurate interference management, making algorithms behave in an overly conservative way. In contrast, the proposed DIA-LS algorithm is based on the formation of individual inhibition areas around every potential receiver node. These inhibition areas are generated according to the physical interference model, providing a more accurate interference management. We first show a constant O(1) approximation bound to the optimal link schedule and demonstrate that our DIA-LS algorithm outperforms the GOW* and the ML2S algorithms, present in the literature.

OOK/DS-CDMA Bit Error Probability over Rayleigh Fading Channels OOK/DS-CDMA Bit Error Probability over Rayleigh Fading Channels

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Date added: 12/30/2013
Date modified: 12/30/2013
Filesize: 286 Bytes
Downloads: 1238

A major constraint in deployments of resource-limited networks is the energy consumption related to the battery lifetime of the network nodes. To this end, power efficient digital modulation techniques such as On-Off keying (OOK) are highly attractive. In this paper, a novel complete probabilistic description of the Direct Sequence - Coded Division Multiple Access (DS-CDMA) system with random signatures employing OOK modulation is presented. The system scenario considers simultaneously transmitting nodes in Rayleigh fading conditions. Numerical simulations are provided to support the derived results.

Effects of Rayleigh-Lognormal fading on IEEE 802.15.4 networks Effects of Rayleigh-Lognormal fading on IEEE 802.15.4 networks

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Date added: 12/30/2013
Date modified: 12/30/2013
Filesize: 286 Bytes
Downloads: 1190

The IEEE 802.15.4 communication protocol is a de-facto standard for wireless applications in industrial and home automation. Although the performance of the medium access control (MAC) of the IEEE 802.15.4 has been thoroughly investigated under the assumption of ideal wireless channel, there is still a lack of understanding of the cross-layer interactions between MAC and physical layer in the presence of realistic wireless channel models that include path loss, multi-path fading and shadowing. In this paper, an analytical model of these dynamics is proposed. The analysis considers simultaneously a composite Rayleigh-lognormal channel fading, interference generated by multiple terminals, the effects induced by hidden terminals, and the MAC reduced carrier sensing capabilities. It is shown that the reliability of the contention-based MAC over fading channels is often far from that derived under ideal channel assumptions. Moreover, it is established to what extent fading may be beneficial for the overall network performance.

Topology optimization for a trade off between energy cost and network lifetime in average consensus Topology optimization for a trade off between energy cost and network lifetime in average consensus

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Date added: 12/30/2013
Date modified: 12/30/2013
Filesize: 286 Bytes
Downloads: 1329

Consensus algorithms are simple processes that involve repeated communications between the nodes of the network until a consensus is reached with certain accuracy. In this setting, the lifetime of the network and the total required energy not only depend on the number of iterations needed to achieve consensus, but also on the power consumption per node and iteration. In this work, we propose a method to optimize the network topology in order to reduce the total energy required to achieve consensus while increasing the network lifetime. Our solution is based on an optimization technique that performs a tradeoff between these two concepts. Simulation results, under different types of networks, are presented to show clearly the efficiency and validity of our approach.

A Wireless Sensor Network Testbed for Event Detection in Smart Homes A Wireless Sensor Network Testbed for Event Detection in Smart Homes

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Date added: 12/30/2013
Date modified: 12/30/2013
Filesize: 286 Bytes
Downloads: 1282

In smart homes, it is essential to reliably detect events including water leakages. A control action, such as shutting the water pipes, relies on reliable event detection. In this demo, a wireless sensor network for detection and localization of events in smart homes is presented. The demo is based on novel distributed detection-estimation and localization algorithms. A graphical user interface to visualize in real-time the network status is developed. Upon a detected event, the user is alerted through a Twitter notification. In the experiments the false alarm probability is improved by 30% and the average relative localization error is 1.7%.

MAC-aware Routing Metrics for Low Power and Lossy Networks MAC-aware Routing Metrics for Low Power and Lossy Networks

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Date added: 12/30/2013
Date modified: 12/30/2013
Filesize: 286 Bytes
Downloads: 1182

In this paper, routing metrics for low power and lossy networks are designed and evaluated. The cross-layer interactions between routing and medium access control (MAC) are explored, by considering the specifications of IETF RPL over the IEEE 802.15.4 MAC. In particular, the experimental study of a reliability metric that extends the expected transmission count (ETX) to include the effects of the level of contention and the parameters at MAC layer is presented. Moreover, a novel metric that guarantees load balancing and increased network lifetime by fulfilling reliability constraints is introduced. The aforementioned metrics are compared to a routing approach based on backpressure mechanism.

Reducing the observation error in a WSN through a consensus-based subspace projection Reducing the observation error in a WSN through a consensus-based subspace projection

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Date added: 12/30/2013
Date modified: 12/30/2013
Filesize: 286 Bytes
Downloads: 1359

An essential process in a Wireless Sensor Network is the noise mitigation of the measured data, by exploiting their spatial correlation. A widely used technique to achieve this reduction is to project the measured data into a proper subspace. We present a low complexity and distributed algorithm to perform this projection. Unlike other algorithms existing in the literature, which require the number of connections at every node to be larger than the dimension of the involved subspace, our algorithm does not require such dense network topologies for its applicability, making it suitable for a larger number of scenarios. Our proposed algorithm is based on the execution of several consensus processes, and therefore the mixing weights that drive the iterative process can be much more easily computed by using information local to each particular node. These two main advantages makes our approach more suitable for large networks composed by simple and power limited nodes. Simulations results are presented to show that our algorithm performs the projection faster and, in several scenarios, consuming less energy than other existing works in the related literature.

Improving reliability and efficiency of communications in WSNs under high traffic demand Improving reliability and efficiency of communications in WSNs under high traffic demand

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Date added: 12/30/2013
Date modified: 12/30/2013
Filesize: 286 Bytes
Downloads: 1197

Carrier Sense Multiple Access protocols are the most widely used methods for collision avoidance in Wireless Sensor Networks (WSNs). These protocols are prone to suffer from the hidden and exposed terminal problems, which lead to inefficiency and unfairness in the communications. Both problems are particularly significant in applications with massive traffic requirements, commonly found in WSNs. The control procedures generally employed to alleviate these effects may lead to performance degradation in the presence of intensive communications. In this paper, we propose a CSMA protocol based on the physical interference model, which mitigates the effect of hidden and exposed terminal problems in a real testbed. Our protocol provides to each pair of transmitter-receiver nodes a different threshold, which determines the maximum tolerated noise for this transmission. No additional control method is used to avoid collisions. Finally, we measure the performance of our protocol by executing over it the average consensus algorithm, which determines the high traffic demand. The packet reception rate, the throughput and the convergence of the consensus algorithm are evaluated in a real testbed.

Energy-efficient Sampling of Networked Control Systems over IEEE 802.15.4 Wireless Networks Energy-efficient Sampling of Networked Control Systems over IEEE 802.15.4 Wireless Networks

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Date added: 12/30/2013
Date modified: 12/30/2013
Filesize: 286 Bytes
Downloads: 1126

Self-triggered sampling is an attractive paradigm for closed-loop control over energy-constrained wireless sensor networks (WSNs) because it may give substantial communication savings. The understanding of the performance of self-triggered control systems when the feedback loops are closed over IEEE 802.15.4 WSNs is of major interest, since the communication standard IEEE 802.15.4 is the de-facto reference protocol for energy-efficient WSNs. In this paper, a new approach to control several processes over a shared IEEE 802.15.4 network by self-triggered sampling is proposed. It is shown that the sampling time of the processes, the protocol parameters, and the scheduling of the transmissions must be jointly selected to achieve a good performance of the closed-loop system and an energy-efficient utilization of the network. The challenging part of the proposed analysis is ensuring globally uniformly ultimately boundedness of the controlled processes while providing efficient scheduling of the process state transmissions. Such a scheduling is difficult when asynchronous multiple control loops share the network, because transmissions over IEEE 802.15.4 are allowed only at certain time slots. The proposed approach establishes that the joint design of self-triggered samplers and the network protocol (1) ensures globally uniformly ultimately boundedness of each control loop, (2) reduces the number of sensor transmissions, and (3) increases the sleep time of the transmitting nodes. A new dynamic scheduling problem is proposed for the joint control of each process and network protocol adaptation. An algorithm is derived, which adapts the network parameters according to the self-triggered sampler of every control loop. Numerical examples illustrate the analysis and show the benefits of the approach. It is concluded that self-triggered control strategies over WSNs ensure desired control performance, reduce the network utilization, and reduce energy consumption only if the protocol parameters are appropriately regulated.