1,720,988 research outputs found
Global stability of a population of mutually coupled oscillators reaching global maximum likelihood estimate through a decentralized approach
No full textOn the optimal relay location and power allocation in a virtual array system with minimum overall outage probability
No full textCooperative communication among terminals allows the achievement of the benefits of MIMO links, such as diversity and multiplexing gains, even with single antenna radio transceivers. In this work we focus on a virtual MIMO link created between a source, cooperating with several relays to form a virtual array, and a destination, equipped with multiple antennas, in a Rayleigh flat-fading scenario. We asses the performance limits of this system, under the non-ergodicity assumption, in terms of outage probability, with the aim to single out the role played by important factors such as the distances between the terminals, power allocation, and time sharing. ©2007 IEEE
Distributed decision through self-synchronizing sensor networks in the presence of propagation delays and asymmetric channels
No full textIn this paper we propose and analyze a distributed algorithm for achieving globally optimal decisions, either estimation or detection, through a self-synchronization mechanism among linearly coupled integrators initialized with local measurements. We model the interaction among the nodes as a directed graph with weights (possibly) dependent on the radio channels, and we pose special attention to the effect of the propagation delay occurring in the exchange of data among sensors, as a function of the network geometry. We derive necessary and sufficient conditions for the proposed system to reach a consensus on globally optimal decision statistics. One of the major results proved in this work is that a consensus is reached with exponential convergence speed for any bounded delay condition if and only if the directed graph is quasi-strongly connected. We provide a closed form expression for the global consensus, showing that the effect of delays is, in general, the introduction of a bias in the final decision. Finally, we exploit our closed form expression to devise a double-step consensus mechanism able to provide an unbiased estimate with minimum extra complexity, without the need to know or estimate the channel parameters
Decentralized detection and localization through sensor networks designed as a population of self-synchronizing oscillators
No full textThe detection and localization of an event through a sensor network is a topic that has attracted considerable attention recently because of many potential applications. Typically, these decisions are taken by conveying the sensor measurements to a sink node that processes the data and provides an estimate. However, the presence of a sink node creates a bottleneck that is the cause of potential congestions and it poses problems of scalability. In this work, we propose a decentralized decision scheme that is capable to achieve optimal decisions without requiring a fusion center. The network is composed of a set of mutually coupled oscillators, where each node is coupled only to the nearest nodes. We show how to achieve optimal detection for both deterministic and random signals by properly selecting the parameters of the coupling mechanism. Furthermore, if the nodes know their own positions and the network is connected, we show how to make each node able to perform a totally distributed energy-based source localization. © 2006 IEEE
Wireless Sensor Networks for Spectrum Sensing to Support Opportunistic Spectrum Access Networks: Protocol Design and Fundamental Trade-offs
No full textSupporting secondary users through a collateral network dedicated to spectrum sensing has been recently proposed as a mean to overcome spectrum sensing limitations of secondary devices. Building on this idea, we propose a protocol for a Wireless Sensor Network (WSN) to support secondary devices of an Opportunistic Spectrum Access (OSA) network. We examine the fundamental tradeoff between the statistics of the primary network traffic for which the WSN is able to support the OSA network and the interference range or, equivalently, the transmit power of secondary transmitters. We optimize the parameters of the proposed protocol to achieve the minimum delay for delivering channel availability information to secondary users, thus maximizing the portion of time they can effectively use idle primary channels to send their data. We further provide simulation results to demonstrate the feasibility and effectiveness of our design, and point at possible research directions to improve the proposed system capabilities
Distributed decision in sensor networks based on local coupling through Pulse Position Modulated signals
No full textIn this work we propose a physical layer design, based on Pulse Position Modulated (PPM) signals, for a decentralized wireless sensor network implementing an iterative consensus algorithm. The proposed scheme does not require any MAC protocol to avoid or resolve collisions, and is also suitable for a half-duplex implementation. The considered network model assumes only local coupling among the nodes, thus allowing for low transmit power even in large scale networks. Furthermore, we show how to remove the effect of propagation delays, multipath, and non perfect synchronization among the nodes, without requiring any channel parameter estimate. As an example of application, we consider a simple parameter estimation problem, which is instrumental to discuss the fundamental trade-offs arising in the system parameters settings, when both observation noise and coupling noise are considered in the performance analysis. ©2008 IEEE
Cognitive WSN transmission control for energy efficiency under WLAN coexistence
No full textIn this paper we design a cognitive access scheme for WSNs that coexist with WLANs, considering the problem of blind and hidden WLAN terminals. The cognitive access scheme relies on a-priory known WLAN idle time distribution functions and repeated channel measurements to optimize the size of the transmitted data unit and the transmission distance, such that the normalized transmission energy is minimized. We compare the proposed scheme with simple carrier sensing and random access solutions and show that the energy gain is significant under typical WLAN utilization values. © 2011 ICST
A Multi-band Noise-aware MAC Protocol for Underwater Acoustic Sensor Networks
No full textWe present a MAC protocol for underwater acoustic sensor networks (UASN) able to overcome the shortcomings induced by the temporary presence of noise sources within, or close-by, the region covered by the UASN. Our solution, named NAMAC for Noise-aware MAC protocol, exploits the ability of nodes equipped with multi-band modems to rapidly switch the frequency band used for communications upon detecting an increase of the in-band noise. Neighboring nodes may collectively decide to migrate to a different band and, as soon as the noise source is no longer impairing communications, to switch back to the default one. NAMAC also ensures connectivity across regions operating on different frequency bands induced by a different impact of noise at different locations. Additionally, if nodes are equipped with acoustic sensors able to monitor low frequencies, i.e., in the range from 0 to 5 kHz, NAMAC can exploit this capability to detect the approaching of a noisy vessel in advance, since noise at low frequencies is audible at larger distances. In this way, nodes can be pre-alerted for a band switch. We perform an extensive comparative performance evaluation of NAMAC based on ns-2 MIRACLE simulations. The noise frequency spectrum used in our simulations reproduces that of existing powerboats. Our performance evaluation shows that NAMAC is able to significantly outperform existing noise unaware MAC protocols that use a single band, increasing the network reliability in the presence of temporary noise sources like passing-by noisy vessels
Distributed decision through self-synchronizing sensor networks in the presence of propagation delays and nonreciprocal channels
No full textIn this paper we propose and analyze a distributed algorithm for achieving globally optimal decisions, either estimation or detection, through a self-synchronization mechanism among linearly coupled integrators initialized with local measurements. We model the interaction among the nodes as a directed graph with weights dependent on the radio interface and we pose special attention to the effect of the propagation delays occurring in the exchange of data among sensors, as a function of the network geometry. We derive necessary and sufficient conditions for the proposed system to reach a consensus on globally optimal decision statistics. One of the major results proved in this work is that a consensus is achieved for any bounded delay condition if and only if the directed graph is quasi-strongly connected. We also provide a closed form expression for the global consensus, showing that the effect of delays is, in general, to introduce a bias in the final decision. The closed form expression is also useful to modify the consensus mechanism in order to get rid of the bias with minimum extra complexity. © 2007 IEEE
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