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ABSTRACT: For secondary usage of spectrum in a cognitive radio system, in order to maintain reliable continuous communication among secondary users, secondary radios need to make contact, communicate and switch to an open RF channel simultaneously when the current channel is reclaimed by a primary user. In this paper, we describe a link maintenance protocol aimed at solving this issue. The communication channel is monitored and dynamically updated based on spectrum availability. Spectral sensing is employed at the receivers to monitor the spectrum and assist in RF channel synchronization between transmitter and receiver. Simulation results characterizing the performance of this protocol are provided. A prototype system with a pair of cognitive radios featuring this protocol is also introduced.
New Frontiers in Dynamic Spectrum Access Networks, 2007. DySPAN 2007. 2nd IEEE International Symposium on; 05/2007
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Vehicular Technology Conference, 2005. VTC-2005-Fall. 2005 IEEE 62nd; 10/2005
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ABSTRACT: Accurate and low-cost sensor localization is a critical requirement for the deployment of wireless sensor networks in a wide variety of applications. In cooperative localization, sensors work together in a peer-to-peer manner to make measurements and then forms a map of the network. Various application requirements influence the design of sensor localization systems. In this article, the authors describe the measurement-based statistical models useful to describe time-of-arrival (TOA), angle-of-arrival (AOA), and received-signal-strength (RSS) measurements in wireless sensor networks. Wideband and ultra-wideband (UWB) measurements, and RF and acoustic media are also discussed. Using the models, the authors have shown the calculation of a Cramer-Rao bound (CRB) on the location estimation precision possible for a given set of measurements. The article briefly surveys a large and growing body of sensor localization algorithms. This article is intended to emphasize the basic statistical signal processing background necessary to understand the state-of-the-art and to make progress in the new and largely open areas of sensor network localization research.
IEEE Signal Processing Magazine 08/2005; · 4.07 Impact Factor
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ABSTRACT: In this paper, we present new analytical, simulated, and experimental results on the performance of relative location estimation in multihop wireless sensor networks. With relative location, node locations are estimated based on the collection of peer-to-peer ranges between nodes and their neighbors using a priori knowledge of the location of a small subset of nodes, called reference nodes. This paper establishes that when applying relative location to multihop networks the resulting location accuracy has a fundamental upper bound that is determined by such system parameters as the number of hops and the number of links to the reference nodes. This is in contrast to the case of single-hop or fully connected systems where increasing the node density results in continuously increasing location accuracy. More specifically, in multihop networks for a fixed number of hops, as sensor nodes are added to the network the overall location accuracy improves converging toward a fixed asymptotic value that is determined by the total number of links to the reference nodes, whereas for a fixed number of links to the reference nodes, the location accuracy of a node decreases the greater the number of hops from the reference nodes. Analytical expressions are derived from one-dimensional networks for these fundamental relationships that are also validated in two-dimensional and three-dimensional networks with simulation and UWB measurement results.
IEEE Journal on Selected Areas in Communications 05/2005; · 3.41 Impact Factor
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ABSTRACT: We present the analytic and simulation results of the performance of relative location estimation in multi-hop wireless sensor networks. It is found that the location estimation accuracy has a fundamental upper boundary. Location accuracy improves by adding more mobile nodes into the network. However, the resulting accuracy converges towards a fixed asymptotic value that is determined by the total number of links to the reference nodes. It is also established that for multi-hop networks, the location accuracy of a node is highly dependent upon the number of hops it is away from the reference nodes. The further away it is from the reference nodes, the worse the location accuracy.
Communications, 2004 IEEE International Conference on; 07/2004
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ABSTRACT: This paper describes an UWB location system that employs relative location principles to provide enhanced location performance in wireless networks. The system takes advantage of peer-to-peer range measurements between the devices and their neighbors. The collective range information is used to jointly estimate the location of the devices in the network providing enhanced performance.
Ultra Wideband Systems and Technologies, 2003 IEEE Conference on; 12/2003
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ABSTRACT: As an optimization problem, precision location requires sufficient constraints to warrant unique location estimation. The algorithm to determine the constraint sufficiency is the locatability algorithm. For the classic triangulation in two dimensions, locatability algorithm examines if a sensor node has at least 3 non-collinear reference node (RN) neighbors. This condition is often not met in most ad hoc sensor networks due to the low RN density. Progressive location was developed to turn a located sensor node into an induced RN which in turn is used to locate other sensor nodes. But even after applying progressive location, a lot of sensor nodes are still left un-locatable. A holistic approach, the rigid body (RB) based location technology, is proposed to group together sensors and RNs in a sensor network to form globally rigid bodies (GRBs) and cooperatively estimate sensor locations. The key differentiator of the technology is its locatability algorithm, a bottom-up procedure to identify GRBs in an anchor-free network and to determine the locatabilities of GRBs by grounding the network. The algorithm consists of four processes (node categorization, bilateration extension, trilateration extension, and tri-connectivity test) and locatability rules. It is shown that a bilateratively rigid sub-network is a strongly rigid graph and requires only the tri-connectivity to become globally rigid. Rules are provided for the locatability determination of rigid bodies and their associated sensor nodes. Simulation results show that the RB-based location algorithm locates drastically more sensor nodes than triangulation and progressive location algorithms especially when RNs are sparse
Networking, Sensing and Control, 2006. ICNSC '06. Proceedings of the 2006 IEEE International Conference on;
