Sema F. Oktug

A Survey of Architectures and Localization Techniques for Underwater Acoustic Sensor Networks

The widespread adoption of the Wireless Sensor Networks (WSNs) in various applications in the terrestrial environment and the rapid advancement of the WSN technology have motivated the development of Underwater Acoustic Sensor Networks (UASNs). UASNs and terrestrial WSNs have several common properties while there are several challenges particular to UASNs that are mostly due to acoustic communications, and inherent mobility. These challenges call for novel architectures and protocols to ensure successful operation of the UASN. Localization is one of the fundamental tasks for UASNs which is required for data tagging, node tracking, target detection, and it can be used for improving the performance of medium access and network protocols. Recently, various UASN architectures and a large number of localization techniques have been proposed. In this paper, we present a comprehensive survey of these architectures and localization methods. To familiarize the reader with the UASNs and localization concepts, we start our paper by providing background information on localization, state-of-the-art oceanographic systems, and the challenges of underwater communications. We then present our detailed survey, followed by a discussion on the performance of the localization techniques and open research issues.

Multi Stage Underwater Sensor Localization Using Mobile Beacons

Underwater sensor networks (USN) are used for harsh oceanographic missions where human operation is dangerous or impossible. Localization is essential for USNs. It is required for data tagging, node tracking and position-based routing algorithms. Localization is challenging because Global Positioning System(GPS) is not available in underwater; at the same time, existing GPS-less schemes based on fixed landmarks have high communication cost. Such cost is critical in mobile underwater sensor networks (MUSN), since sensor nodes drift with the ocean currents, thus requiring continuous refresh. In this paper, we propose a multi-stage localization scheme using mobile beacons. The beacons periodically ascent and descent in the water column. When they resurface, they receive new GPS coordinates. Then, they dive to the level of the underwater sensors to advertise these coordinates. In turn, localized sensors become proxy beacons and propagate their own coordinates, etc. This iterative, multi-stage localization is the major innovation of this paper. The goal is to localize the nodes with the smallest number of beacons using proxies instead, yet achieving an adequate accuracy. The major benefit is the reduction in operating costs. Mobility is a critical factor in determining performance. In this paper, performance (i.e., the percentage of localized nodes during a cycle, accuracy, delay and communication cost) is tested in a simulation scenario based on a realistic mobility model. The meandering current mobility with surface effect (MCM-SE) model - a composite model combining surface and subsurface currents.

Localization techniques for underwater acoustic sensor networks

Underwater acoustic sensor networking is the enabling technology for a wide range of applications including naval surveillance, oil platform monitoring, earthquake and tsunami forewarning, climate and ocean observation, and water pollution tracking. Underwater sensor nodes with sensing and communication capabilities form the underwater acoustic sensor network. Localizing the underwater sensor nodes is one of the fundamental tasks for UASNs where the location information can be used in data tagging, routing, and node tracking. Localization for UASNs is an active research topic where a large number of techniques have been proposed recently. This article provides an up-to-date survey of these techniques while pointing out the open issues.

Primary user activity modeling using first-difference filter clustering and correlation in cognitive radio networks

In many recent studies on cognitive radio (CR) networks, the primary user activity is assumed to follow the Poisson traffic model with exponentially distributed interarrivals. The Poisson modeling may lead to cases where primary user activities are modeled as smooth and burst-free traffic. As a result, this may cause the cognitive radio users to miss some available but unutilized spectrum, leading to lower throughput and high false-alarm probabilities. The main contribution of this paper is to propose a novel model to parametrize the primary user traffic in a more efficient and accurate way in order to overcome the drawbacks of the Poisson modeling. The proposed model makes this possible by arranging the first-difference filtered and correlated primary user data into clusters. In this paper, a new metric called the Primary User Activity Index, , is introduced, which accounts for the relation between the cluster filter output and correlation statistics. The performance of the proposed model is evaluated by means of traffic estimation accuracy, false-alarm probabilities while keeping the detection probability of primary users at a constant value. Simulation results show that the appropriate selection of the Primary User Activity Index, higher primary-user detection accuracy, reduced false-alarm probabilities, and higher throughput can be achieved by the proposed model.

Localization in Wireless Sensor Networks with Range Measurement Errors

In sensor networks, data collected by sensor nodes needs to be tagged with time and location information. Localization techniques are used to determine the location information by estimating location of a sensor node. It is well known that distance measurement errors affect the accuracy of estimated location. These errors may be due to methodical or environmental factors. In this paper, we propose AML (Adapted Multi-Lateration) by improving the existing multi-lateration technique. It is shown that the AML method is more robust to measurement errors; its mean localization error is lower than the multi-lateration technique for noisy measurements. Besides, the time complexity of the AML method is less than the multi-lateration technique since it does not require to solve the normal equation for the linear least squares problem as in the multi-lateration technique. Additionally, AML is advantageous for iterative localization where localized nodes become reference nodes and employed in the localization process. Incorporating these reference nodes in the AML equations is easier than multi-lateration technique.

Design and performance evaluation of a banyan network based interconnection structure for ATM switches

This paper presents a new self-routing packet network called the plane interconnected parallel network (PIPN). In the proposed design, the traffic arriving at the network is shaped and routed through two banyan network based interconnected planes. The interconnections between the planes distribute the incoming load more homogeneously over the network. The throughput of the network under uniform and heterogeneous traffic requirements is studied analytically and by simulation. The results are compared with the results of the baseline network and another banyan network based parallel interconnection network. It is shown that, for the proposed design, a higher degree of heterogeneity results in better performance.

A localization and routing framework for mobile underwater sensor networks

In this paper, we propose a framework to establish localization and routing in mobile underwater sensor networks. Localization and routing are done at two consecutive rounds. Localization messages include localization specific data and additional fields which are used in the routing decision. The proposed catch up or pass forwarding algorithm is a greedy geo-forwarding scheme. It benefits from the uncontrolled motion of the underwater nodes. The underwater nodes use position and velocity information to decide whether to carry the packet until they catch up with a sink or pass it to a faster or slower relay.

3D Coverage Analysis under Heterogeneous Deployment Strategies in Wireless Sensor Networks

In this paper, we propose novel deployment strategies for Wireless Sensor Networks and study 3D coverage under these heterogeneous deployment strategies. Our aim is to find answers to questions like how many sensors are needed to cover a specified 3D terrain at a specified coverage percentage. Furthermore, the effect of sleeping on coverage is also studied. Simulation results demonstrate that depending on application requirements an appropriate deployment strategy can be selected to obtain required 3D coverage.

Periodicity-Based Anomalies in Self-Similar Network Traffic Flow Measurements

Network traffic flow measurement is fundamental in timely monitoring computer networks and in diagnosing potential anomalies. Previous measurement studies have shown that network traffic flows are often self-similar. The degree of self-similarity is described by the Hurst parameter H. In the literature, various methods have been used in estimating H, while their performances have not been evaluated for network traces that contain periodicity-based anomalies. In this paper, we investigate the performance of well-known estimators for traffic flow measurements with periodicity-based anomalies. We derive analytical expressions for widely used estimation methods in time, frequency, wavelet, and eigen domains and demonstrate through simulations that periodicity-based anomalies affect Hurst parameter estimation, causing unreliable H estimates. We show that our theoretical and experimental results are consistent with the observations of real network traffic flow measurements.

Analyzing the effects of burst assembly in optical burst switching under self-similar traffic

Optical burst switching is a novel switching concept which is a hybrid of optical packet switching and optical wavelength routing. In order to provide an efficient bandwidth utilization, various burst assembly and scheduling schemes for optical bursts are introduced. In this work, the effects of burst assembly techniques on the performance of the optical burst switching (OBS) technique and the characteristics of the network traffic are studied. In order to assemble IP packets to form optical bursts, a time threshold based technique and a hybrid technique, which is based on both time and size threshold, are employed. Self-similar IP traffic is applied to the ingress nodes of the optical network. The effects of the burst assembly algorithms, just after the bursts are formed, are studied in detail considering self-similarity, burst size, and burst formation delay. The performance of the horizon scheduling technique is studied under both burst assembly methods. Moreover, the characteristics of the traffic obtained at the egress nodes are studied in terms of burst size, and self-similarity.