The development of practical, localized algorithms is probably the most needed and most challenging task in wireless ad-hoc sensor networks (WASNs). Localized algorithms are a special type of distributed algorithms where only a subset of nodes in the WASN participate in sensing, communication, and computation. We have developed a generic localized algorithm for solving optimization problems in wireless ad-hoc networks that has five components: (i) data acquisition mechanism, (ii) optimization mechanism, (iii) search expansion rules, (iv) bounding conditions, and (v) termination rules. The main idea is to request and process data only locally and only from nodes who are likely to contribute to rapid formation of the final solution. The approach enables two types of optimization: The first, guarantees the fraction of nodes that are contacted while optimizing for solution quality. The second, provides guarantees on solution quality while minimizing the number of nodes that are contacted and/or amount of communication. This localized optimization approach is applied to two fundamental problems in sensor networks: location discovery and exposure-based coverage. We demonstrate its effectiveness on a number of examples.

Topology control, wherein nodes adjust their transmitting ranges to conserve energy, is an important feature in wireless ad hoc networks. In this paper, we present a topology control protocol that is fully distributed, asynchronous, and localized. This protocol, referred to as the k-NEIGH protocol, maintains the number of neighbors of every node equal to or slightly below a specific value k. Furthermore, the protocol ensures that the resulting communication graph is symmetric, thereby easing the operation of higher protocol layers. To evaluate the performance of the protocol, the value of k that ensures a connected communication graph with high probability is evaluated. It is also shown that, with n nodes in the network, the protocol terminates on every node after exactly 2n messages total and within strictly bounded time. Finally, extensive simulations are carried out, which show that the k-NEIGH protocol is about 20% more energy-efficient than the most widely-studied existing protocol.

Abstract — In this paper, we present a novel time-based positioning scheme (TPS) for efficient location discovery in outdoor sensor networks. TPS relies on TDoA (Time-Difference-of-Arrival) of RF signals measured locally at a sensor to detect range differences from the sensor to three base stations. These range differences are averaged over multiple beacon intervals before they are combined to estimate the sensor location through trilateration. A nice feature of this positioning scheme is that it is purely localized: sensors independently compute their positions. We present a statistical analysis of the performance of TPS in noisy environments. We also identify possible sources of position errors with suggested measures to mitigate them. Our scheme requires no time synchronization in the network and minimal extra hardware in sensor construction. TPS induces no communication overhead for sensors, as they listen to three beacon signals passively during each beacon interval. The computation overhead is low, as the location detection algorithm involves only simple algebraic operations over scalar values. TPS is not adversely affected by increasing network size or density and thus offers scalability. We conduct extensive simulations to test the performance of TPS when TDoA measurement errors are normally distributed or uniformly distributed. The obtained results show that TPS is an effective scheme for outdoor sensor self-positioning. I.

Abstract – Fine-grained geographic localization of nodes is essential for an extensive range of distributed sensor applications. To compute geographic coordinates, localization algorithms commonly use pair-wise distance estimates between nodes. In this paper we present a noise tolerant acoustic ranging mechanism for wireless sensors that employs digital signal processing techniques on standard MICA hardware. We describe how noise canceling, digital filtering and peak detection can be applied to meet the severe resource constraints of the platform, yet yielding average range estimation errors below 10cm independently from the actual node-to-node distances.

Ultrasonic location systems are a popular solution for the provision of fine-grained indoor positioning data. Applications include enhanced routing for wireless networks, computer-aided navigation, and location-sensitive device behavior. However, current ultrasonic location systems suffer from limitations due to their use of narrowband transducers. This paper investigates the use of broadband ultrasound for indoor positioning systems. Broadband ultrasonic transmitter and receiver units have been developed and characterized. The utilization of these units to construct two positioning systems with different architectures serves to highlight and affirm the concrete, practical benefits of broadband ultrasound for locating people and devices indoors.

Realistic, complex, outdoor environments pose significant challenges for node localization in Wireless Sensor Networks. In spite of the fact that many elegant and clever solutions have been proposed, no robust localization system has emerged. This status quo is because existing solutions work well for single sets of assumptions which, however, do not always hold in complex environments. In this article, we review the state of art for node localization in Wireless Sensor Networks and show how localization protocol composability has the potential to provide the robust solution that is needed. By composing localization protocols in a hierarchy and allowing the execution of multiple localization schemes, robust solutions against any single protocol failure can be built. 1

Abstract--Localization for outdoor wireless sensor networks has been a challenge for real applications. Although many solutions have been proposed, few of them can be used in real applications because of their high cost, low accuracy or infeasibility due to practical issues. In this paper, we propose a practical acoustic localization scheme called Thunder. Thunder employs an asymmetric architecture and shifts most of the complexities and hardware requirements from each node to a single powerful centralized device. The solution is efficient, and requires virtually zero cost in terms of extra per node hardware and in-network communication. This paper also presents an efficient scheduling algorithm called Equilateral Triangle Scheduling to schedule Thunder for very large sensor networks and a resilient algorithm called Adaptive Fuzzy Clustering to provide robust localization without sacrificing efficiency in the presence of a high percentage of large ranging errors. To validate and evaluate Thunder, we built an experimental localization system based on the Mica2 platform, which achieved localization errors of about 1 meter in medium scale localization experiments. Localization for outdoor wireless sensor

In this paper, we present Probabilistic Geographic Routing (PGR), a novel approach for the problem of power-aware routing in wireless ad hoc and sensor networks. Our protocol uses only local information to probabilistically forward the packet to the next hop. Every node relies on a beaconing process to keep track of the changes in the set of its neighbors. In order to forward a packet, the node selects a set of candidate nodes. These candidate nodes are then assigned a probability proportional to their residual energy and the link reliability. We have implemented PGR in NS-2 and compared the performance to two existing protocols, GPSR and Probabilistic Flooding. Based on the simulation results, PGR improves the throughput by 40%, increases the lifetime of the network by 30%, and decreases the overall end-to-end delay. In addition, we have implemented PGR on a real sensor network test-bed to verify our protocol. 1.

Abstract--Localization for wide area wireless sensor networks has been a practical challenge for real applications. Although many solutions have been proposed, few of them can be used in real applications due to their high cost (requirements on extra hardware), low accuracy or infeasibility due to practical issues. In this paper, we propose a practical acoustic localization scheme called Thunder, which can achieve high accuracy without requiring any extra hardware to current popular sensor platforms, such as the MICA2. We evaluate our scheme with MICA2 motes which are deployed in a 24.4m × 68.6m area in a parking lot, and achieve localization errors of about 1 meter, by using a centralized device mainly comprised of a speaker. The solution is efficient, uses minimal energy and completes in a couple of minutes. 1.

Realistic, complex outdoor environments pose significant challenges for node localization in wireless sensor networks. In spite of the fact that many elegant and clever solutions have been proposed, no robust localization system has emerged. This status quo is because existing solutions work well for single sets of assumptions that, however, do not always hold in complex environments. In this article we review the state of the art for node localization in wireless sensor networks and show how localization protocol composability has the potential to provide the robust solution that is needed. By composing localization protocols in a hierarchy and allowing the execution of multiple localization schemes, robust solutions against any single protocol failure can be built. W ireless sensor network (WSN) systems have recently been developed for several domains: military surveillance, environmental