A State-of-the-Art Survey on Multidimensional Scaling-Based Localization Techniques <s> 1) Time of Arrival (ToA) Estimation: <s> With the advances in wireless communications and low-power electronics, accurate position location may now be accomplished by a number of techniques which involve commercial wireless services. Emerging position location systems, when used in conjunction with mobile communications services, will lead to enhanced public safety and revolutionary products and services. The fundamental technical challenges and business motivations behind wireless position location systems are described, and promising techniques for solving the practical position location problem are treated. <s> BIB001 </s> A State-of-the-Art Survey on Multidimensional Scaling-Based Localization Techniques <s> 1) Time of Arrival (ToA) Estimation: <s> This paper presents the design, implementation, and evaluation of Cricket , a location-support system for in-building, mobile, location-dependent applications. It allows applications running on mobile and static nodes to learn their physical location by using listeners that hear and analyze information from beacons spread throughout the building. Cricket is the result of several design goals, including user privacy, decentralized administration, network heterogeneity, and low cost. Rather than explicitly tracking user location, Cricket helps devices learn where they are and lets them decide whom to advertise this information to; it does not rely on any centralized management or control and there is no explicit coordination between beacons; it provides information to devices regardless of their type of network connectivity; and each Cricket device is made from off-the-shelf components and costs less than U.S. $10. We describe the randomized algorithm used by beacons to transmit information, the use of concurrent radio and ultrasonic signals to infer distance, the listener inference algorithms to overcome multipath and interference, and practical beacon configuration and positioning techniques that improve accuracy. Our experience with Cricket shows that several location-dependent applications such as in-building active maps and device control can be developed with little effort or manual configuration. <s> BIB002 </s> A State-of-the-Art Survey on Multidimensional Scaling-Based Localization Techniques <s> 1) Time of Arrival (ToA) Estimation: <s> The development of architectures and strategies that allow for rapid and cost-effective deployment of large scale geographically distributed sensor based systems that organize themselves in an ad hoc fashion in order to improve the monitoring and detection capabilities, is becoming more a requirement rather than a desire. In this paper, we first provide a model that characterizes the corresponding sensor connectivity distribution for a sensor networking system, and based on this model we gain some insight about the trade off among the node connectivity, power consumption, data rate, etc. The impact of node connectivity on system reliability is discussed. Furthermore in order to reduce the sensor power consumption we analyze the relationship between periodical sleeping strategies and the achieved power conservation. Several results and tradeoffs among various sleeping strategies, transmission scenarios and power gains, for given connectivity requirements, are also presented and evaluated. <s> BIB003 </s> A State-of-the-Art Survey on Multidimensional Scaling-Based Localization Techniques <s> 1) Time of Arrival (ToA) Estimation: <s> Localization (a.k.a. locationing) is a central concern for ubiquitous self-configuring sensor networks. In this paper the implementation of a distributed, least-squares-based localization algorithm is presented. Low power and energy dissipation are key requirements for sensor networks. As part of the sensor network, the localization system must also conform to these requirements. An ultra-low-power and dedicated hardware implementation of the localization system is therefore presented. The cost of fixed-point implementation is also investigated. The design is implemented in a 0.13 /spl mu/ CMOS process. It dissipates 1.7 mW of active power and 0.122 J/op of active energy with a silicon area of 0.55 mm/sup 2/. The mean calculated location error due to fixed-point implementation is shown to be 6%. <s> BIB004 </s> A State-of-the-Art Survey on Multidimensional Scaling-Based Localization Techniques <s> 1) Time of Arrival (ToA) Estimation: <s> Localization of a wireless device using the time-of-arrivals (TOAs) from different base stations has been studied extensively in the literature. Numerous localization algorithms with different accuracies, computational complexities, a-priori knowledge requirements, and different levels of robustness against non-line-of-sight (NLOS) bias effects also have been reported. However, to our best knowledge, a detailed unified survey of different localization and NLOS mitigation algorithms is not available in the literature. This paper aims to give a comprehensive review of these different TOA-based localization algorithms and their technical challenges, and to point out possible future research directions. Firstly, fundamental lower bounds and some practical estimators that achieve close to these bounds are summarized for line-of-sight (LOS) scenarios. Then, after giving the fundamental lower bounds for NLOS systems, different NLOS mitigation techniques are classified and summarized. Simulation results are also provided in order to compare the performance of various techniques. Finally, a table that summarizes the key characteristics of the investigated techniques is provided to conclude the paper. <s> BIB005 </s> A State-of-the-Art Survey on Multidimensional Scaling-Based Localization Techniques <s> 1) Time of Arrival (ToA) Estimation: <s> Advancements in information technology and communication systems enabled the development of a wide variety of location based applications and services. The global navigation satellite systems are among the fundamental localization solutions. In harsh environments (e.g., urban canyons and indoor areas), these solutions do not provide a good accuracy or even become unavailable. In order to offer accurate and ubiquitous localization solutions, wireless communication systems have been considered, where several location dependent parameters of the transmitted signals can be measured and exploited (e.g., the time-of-arrival (ToA), the received signal strength (RSS)). In this work, the topic of wireless localization is explored from a statistical signal processing perspective with a focus on two axes. The first axis is cooperative localization applied to ad-hoc networks, where the nodes perform pair-wise ranging measurements (i.e., ToA or RSS) between each other in order to simultaneously estimate their positions. The unique solvability conditions are studied based on the two approaches of graph rigidity and semidefinite programming, and the identifiability conditions are derived. Location estimation solutions are considered with a focus on probabilistic estimation and its application in Markov random fields using the nonparametric belief propagation (NBP) algorithm. The second axis is mobile terminals tracking based on RSS measurements. These measurements are affected by a shadowing phenomenon. The improvement brought by the knowledge of the shadowing maps to the position estimation accuracy is studied. The classical solution for obtaining these maps is fingerprinting, which can be costly in time and effort. Solutions are developed to overcome these difficulties. Several solutions are proposed and investigated via Monte Carlo simulations in different deployment and application scenarios, and several theoretical and practical results are derived. <s> BIB006 </s> A State-of-the-Art Survey on Multidimensional Scaling-Based Localization Techniques <s> 1) Time of Arrival (ToA) Estimation: <s> The distance estimation between nodes is a crucial requirement for localization and object tracking. Received signal strength (RSS) measurement is one of the used methods for the distance estimation in wireless networks. Its main advantage is that there are no additional hardware requirements. This paper describes a lateration approach for localization and distance estimation using RSS. For the purpose of investigation of RSS uncertainty, several scenarios were designed for both indoor and outdoor measurements. The first set of RSS measurement scenarios was proposed with the intention of hardware independent investigation of radio channel. For the second set of measurements, we employed IRIS sensor nodes to evaluate the distance estimation with certain devices. The experiments considered also obstacles in the radio channel. The results obtained in the proposed scenarios present usability of the method under different conditions. There is also a signal propagation model constructed from measured data at a node, which subsequently serves for distance determination. <s> BIB007
ToA is one of the most widely used ranging techniques for positioning systems. In ToA based positioning systems, users computes the time delay of signal propagation to estimate the distance between the receiver and the transmitter. The main problem with ToA measurements is that the received signal arrives through multipath with different delay through the channel BIB005 . LoS signal is presumed to be available in ToA systems to compute the signal propagation delay  . In ToA systems setup, the anchors broadcast the beacon signal while the node (or user) computes propagation delay of the received signal from multiple anchors. The transmitted signal travels with the speed of light and thus, the distance between node and anchor is estimated from the propagation delay. The intersection of the circles from different anchors leads to the region of estimated position of a node. But due to different environmental effects, the signal arrives at the node at multiple paths with different delays BIB004 . Therefore, multipath leads to an error in position estimation, because the circles from different anchors do not intersect at a single point  . 2) Time Difference of Arrival (TDoA) Estimation: TDoA is an enhanced version of ToA technique where a node estimates the distance by receiving two different kinds of signals from the same anchor or same type of signal from two different anchors. Cricket system BIB002 is a good example of TDoA based indoor localization system which uses ultrasound signals and RF signals for localization. The time difference between the two signals is calculated by the receiver and generates a hyperbola BIB001 . The point where the hyperbolas from different anchors intersect yields to the node position. In comparison to the ToA measurements, the TDoA does not require synchronization between the anchors and the node BIB006 . But using two different kinds of signals for localization leads to a higher cost due to the extra hardware required to transmit and receive two different kinds of signals. 3) Received Signal Strength (RSS) Estimation: Received signal strength (RSS) measurements are the simplest and most commonly used technique for distance estimation BIB007 . The free space path loss model is usually used to estimate the distance from the measured received power  . The strength of a received signal is decreased due to path loss, frequency selective fading, and shadowing. The effect of path loss is to be measured, as it is a deterministic decrease in power as a function of the distance between the node and the anchor. Multipath fading, in spite of being problematic, is deemed advantageous. This fading is produced by either constructive or destructive addition of time-delayed signals at various frequencies. Therefore, the correlation between the estimations is less if the estimations are carried out at different frequencies that are separated beyond the coherence bandwidth. Furthermore, multiple spread-spectrum wireless sensors will be employed that will average out frequency selective fading. Unfavorably, the same technique is not present to counter shadowing, which is most of the times introduced by object blockage between the node and the anchors. The received power P r (d ) at distance d can be written as BIB003  where P r (d 0 ) represents the power received at reference distance d 0 and η is the path loss exponent.