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The information available to connectivity-based positioning algorithms is the radio range of sensor devices and the position estimates of neighbors and neighbors of neighbors. This information creates special graph theoretic structures which impose new constraints on the positions of sensor devices. The new constraints sometimes lead to a feasible set of positions with disconnected regions. These properties can be used to reduce the set of feasible positions for a node. In this paper, a new fully distributed positioning algorithm, called Orbit, which exploits these properties is presented for mobile sensor networks. The algorithm uses additional constraints and trims disconnected regions. These new constraints are generated through cooperation between neighbors. The performance of Orbit is examined for many communication and mobility models, including a probabilistic communication model generated from radio experiments. Computer simulation experiments demonstrate that Orbit outperforms a recently proposed positioning algorithm in terms of positional accuracy under different models with a wide range of parameter values. Orbit is implemented on resource limited sensor devices. This implementation demonstrates the feasibility of the algorithm for sensor devices. The algorithm is tested on deployments of the sensor devices in a field and the results are comparable to those from the simulation experiments. [ABSTRACT FROM AUTHOR]

Abstract: The positioning of wireless nodes has been an active research area over the last decade. Many network positioning algorithms have been proposed to solve this problem. The vast majority assume that a fixed set of nodes (called seeds) have a mechanism to position themselves at all times (using GPS or other means). The other nodes estimate their positions based on positional information exchanged between nodes using wireless communication. The monetary cost of a GPS unit is decreasing so systems where most nodes are equipped with a GPS unit is foreseeable. A problem with this assumption is that the task of self-positioning via a GPS unit is expensive in terms of energy consumption which results in faster battery decay. In this paper, we assume that every node is capable of self-positioning but activates that module selectively. This allows for balancing the energy costs of self-positioning among all nodes and results in reduced positional error. We investigate several different strategies for governing the self-positioning module and report on their performance. [Copyright &y& Elsevier]

Abstract: Localization is defined as the problem of determining the geographical locations of nodes in a wireless ad hoc or sensor network. Networks typically have some nodes (called seeds) that know their locations (using GPS or other means). Other (non-seed) nodes compute their locations by exchanging messages with nodes within their radio range.Several algorithms have been proposed for localization in different scenarios. Algorithms have been designed for networks in which each node has ranging capabilities (i.e., can estimate distances to its neighbors). Other algorithms have been proposed for networks in which no node has such capabilities. Some algorithms only work when nodes are static. Some other algorithms are designed specifically for networks in which all nodes are mobile. In this paper we propose a range-based localization algorithm RMCB for wireless sensor networks. Our algorithm uses a small fraction of seeds. It also makes use of the received signal strength measurements that are available from the sensor hardware. Our algorithm works well when nodes are static or mobile. We demonstrate using empirical data from sensor hardware (Texas Instruments EZ 430-RF2500) and simulations that RMCB outperforms a very good range-free algorithm WMCL in terms of localization error and has a similar computational complexity to WMCL. [Copyright &y& Elsevier]

Abstract: A very important problem in many wireless ad-hoc networks, including wireless sensor networks, is positioning or the determination of geographical locations of the wireless nodes. Positioning is used both in infrastructural aspects of sensor networks, like geographic routing and topology maintenance, and in applications like wildlife tracking. Connectivity-based positioning algorithms in mobile wireless systems are studied in this work. These algorithms compute node positions based only on the connectivity, i.e. the neighborhood information of each node. Many algorithms have been proposed for positioning in stationary node systems and bounds on positional error of algorithms have been derived. The design and analysis of positioning algorithms for mobile node systems is a more challenging problem. Node mobility increases the amount of positional information available to a positioning algorithm. The work in this paper establishes a bound on the positional error for connectivity-based algorithms in mobile systems. The formulation from the analysis is used to investigate the benefit of this additional positional information on reducing positional error. There is a limit to the usefulness of positional information from previous node positions due to movement. This captures an important performance tradeoff: historical positional information can yield reduced positional error but requires more connectivity information from the network which requires greater computational resources. [Copyright &y& Elsevier]