A survey and comparison on localisation algorithms for wireless ad hoc networks <s> Introduction <s> The problem of bearings-only target localization is to estimate the location of a fixed target from a sequence of noisy bearing measurements. Although, in theory, this process is observable even without an observer maneuver, estimation performance (i.e., accuracy, stability and convergence rate) can be greatly enhanced by properly exploiting observer motion to increase observability. This work addresses the optimization of observer trajectories for bearings-only fixed-target localization. The approach presented herein is based on maximizing the determinant of the Fisher information matrix (FIM), subject to state constraints imposed on the observer trajectory (e.g., by the target defense system). Direct optimal control numerical schemes, including the recently introduced differential inclusion (DI) method, are used to solve the resulting optimal control problem. Computer simulations, utilizing the familiar Stansfield and maximum likelihood (ML) estimators, demonstrate the enhancement to target position estimability using the optimal observer trajectories. <s> BIB001 </s> A survey and comparison on localisation algorithms for wireless ad hoc networks <s> Introduction <s> This article considers the importance of context in mobile systems. It considers a range of context-related issues and focus on location as a key issue for mobile systems. A design framework is described consisting of taxonomies of location, mobility, population, and device awareness. The design framework inorms the construction of a semantic model of space for mobile systems. The semantic model is reflected in a computational model built on a distriuted platform that allows contextual information to be shared across a number of mobile devices. The framework support the design of interactive mobile systems while the platform supports their rapid development. <s> BIB002 </s> A survey and comparison on localisation algorithms for wireless ad hoc networks <s> Introduction <s> We describe Environmental Observation and Forecasting Systems (EOFS), a new class of large-scale distributed system designed to monitor, model, and forecast wide-area physical processes such as river systems. EOFS have strong social relevance in areas such as education, transportation, agriculture, natural resource planning and disaster response. In addition, they represent an opportunity for scientists to study large physical systems to an extent that was not previously possible. Building the next generation of EOFS pose a number of difficult challenges in all aspects of wireless networking, including media protocols for long distance vertical communication through water, flooding algorithms in ad-hoc network topologies, support for rate- and time-sensitive applications, and location-dependent mobile computing. <s> BIB003 </s> A survey and comparison on localisation algorithms for wireless ad hoc networks <s> Introduction <s> We present Greedy Perimeter Stateless Routing (GPSR), a novel routing protocol for wireless datagram networks that uses the positions of routers and a packet's destination to make packet forwarding decisions. GPSR makes greedy forwarding decisions using only information about a router's immediate neighbors in the network topology. When a packet reaches a region where greedy forwarding is impossible, the algorithm recovers by routing around the perimeter of the region. By keeping state only about the local topology, GPSR scales better in per-router state than shortest-path and ad-hoc routing protocols as the number of network destinations increases. Under mobility's frequent topology changes, GPSR can use local topology information to find correct new routes quickly. We describe the GPSR protocol, and use extensive simulation of mobile wireless networks to compare its performance with that of Dynamic Source Routing. Our simulations demonstrate GPSR's scalability on densely deployed wireless networks. <s> BIB004 </s> A survey and comparison on localisation algorithms for wireless ad hoc networks <s> Introduction <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> BIB005 </s> A survey and comparison on localisation algorithms for wireless ad hoc networks <s> Introduction <s> The proliferation of mobile computing devices and local-area wireless networks has fostered a growing interest in location-aware systems and services. In this paper we present RADAR, a radio-frequency (RF)-based system for locating and tracking users inside buildings. RADAR operates by recording and processing signal strength information at multiple base stations positioned to provide overlapping coverage in the area of interest. It combines empirical measurements with signal propagation modeling to determine user location and thereby enable location-aware services and applications. We present experimental results that demonstrate the ability of RADAR to estimate user location with a high degree of accuracy. <s> BIB006 </s> A survey and comparison on localisation algorithms for wireless ad hoc networks <s> Introduction <s> Wireless ad-hoc sensor networks will provide one of the missing connections between the Internet and the physical world. One of the fundamental problems in sensor networks is the calculation of coverage. Exposure is directly related to coverage in that it is a measure of how well an object, moving on an arbitrary path, can be observed by the sensor network over a period of time. In addition to the informal definition, we formally define exposure and study its properties. We have developed an efficient and effective algorithm for exposure calculation in sensor networks, specifically for finding minimal exposure paths. The minimal exposure path provides valuable information about the worst case exposure-based coverage in sensor networks. The algorithm works for any given distribution of sensors, sensor and intensity models, and characteristics of the network. It provides an unbounded level of accuracy as a function of run time and storage. We provide an extensive collection of experimental results and study the scaling behavior of exposure and the proposed algorithm for its calculation. <s> BIB007 </s> A survey and comparison on localisation algorithms for wireless ad hoc networks <s> Introduction <s> As new fabrication and integration technologies reduce the cost and size of micro-sensors and wireless interfaces, it becomes feasible to deploy densely distributed wireless networks of sensors and actuators. These systems promise to revolutionize biological, earth, and environmental monitoring applications, providing data at granularities unrealizable by other means. In addition to the challenges of miniaturization, new system architectures and new network algorithms must be developed to transform the vast quantity of raw sensor data into a manageable stream of high-level data. To address this, we propose a tiered system architecture in which data collected at numerous, inexpensive sensor nodes is filtered by local processing on its way through to larger, more capable and more expensive nodes.We briefly describe Habitat monitoring as our motivating application and introduce initial system building blocks designed to support this application. The remainder of the paper presents details of our experimental platform. <s> BIB008 </s> A survey and comparison on localisation algorithms for wireless ad hoc networks <s> Introduction <s> Many ad hoc network protocols and applications assume the knowledge of geographic location of nodes. The absolute location of each networked node is an assumed fact by most sensor networks which can then present the sensed information on a geographical map. Finding location without the aid of GPS in each node of an ad hoc network is important in cases where GPS is either not accessible, or not practical to use due to power, form factor or line of sight conditions. Location would also enable routing in sufficiently isotropic large networks, without the use of large routing tables. We are proposing APS - a distributed, hop by hop positioning algorithm, that works as an extension of both distance vector routing and GPS positioning in order to provide approximate location for all nodes in a network where only a limited fraction of nodes have self location capability. <s> BIB009 </s> A survey and comparison on localisation algorithms for wireless ad hoc networks <s> Introduction <s> We consider the problem of node positioning in ad-hoc networks. We propose a distributed, infrastructure-free positioning algorithm that does not rely on Global Positioning System (GPS). The algorithm uses the distances between the nodes to build a relative coordinate system in which the node positions are computed in two dimensions. The main contribution of this work is to define and compute relative positions of the nodes in an ad-hoc network without using GPS. We further explain how the proposed approach can be applied to wide area ad-hoc networks. <s> BIB010 </s> A survey and comparison on localisation algorithms for wireless ad hoc networks <s> Introduction <s> Today's wireless devices have the capability to receive information that is tailored to customers' needs at a particular location. A unique set of location-based services--called PNT and including user-solicited information, worldwide mapping, route guidance, positioning and ecouponing -- has been created for tiny displays and limited input of mobile Internet-enabled cellular phones. A first version is available on an Ericsson R380s. A set of user interfaces has been designed. This makes finding information more intuitive than ever before: interfaces have been optimized for mobile use that demands not only quick and direct manipulation but also easy navigation. <s> BIB011 </s> A survey and comparison on localisation algorithms for wireless ad hoc networks <s> Introduction <s> Time-difference of arrival (TDOA) estimates are an attractive means for geolocation of targets via low-cost, distributed, single-element acoustic sensors. Relative to distributed beamforming approaches. TDOA localization requires significantly less bandwidth between sensor nodes and exhibits greater tolerance to uncertainties in sensor node location and data synchronization. In this paper, we present algorithms for estimating TDOA over low-bandwidth links, and for combining these estimates to provide geolocation of targets. Both of these components are adapted specifically to operation in a low-power, low-bandwidth distributed sensor environment. TDOA estimation is performed using spectral peaks from the acoustic signals, which allows drastic reduction in the bandwidth required to collaboratively determine bearing to target. Previously published localization algorithms were modified to minimize the required communication bandwidth and to support scaling of the algorithm to many distributed nodes. The performance of the various localization algorithms is simulated and compared for several scenarios. The preferred algorithms are also applied to pre-recorded field data and the resulting geolocation estimates are compared to ground truth data. <s> BIB012 </s> A survey and comparison on localisation algorithms for wireless ad hoc networks <s> Introduction <s> We present an algorithm for locating and orienting a set of sensor arrays that have been deployed in a scene at unknown locations and orientation angles. This self-calibration problem is solved using a number of source signals also deployed in the scene. We assume each array can estimate the time-of-arrival and direction-of-arrival of every source. From this information we compute the array locations and orientations. We consider four subproblems, in which the source signals or emission times are either known or unknown. We develop necessary conditions for solving the self-calibration problem and provide a maximum likelihood solution and corresponding location error estimate. <s> BIB013 </s> A survey and comparison on localisation algorithms for wireless ad hoc networks <s> Introduction <s> Group communication has become increasingly important in mobile ad hoc networks (MANET). Current multicast routing protocols in MANET have a large overhead due to the dynamic network topology. To overcome this problem, there is a recent shift towards stateless multicast in small groups. We introduce a small group multicast scheme, based on packet encapsulation, which uses a novel packet distribution tree construction algorithms for efficient data delivery. The tree is constructed with the goal of minimizing the overall bandwidth cost of the tree. Two construction algorithms, for a location-guided k-ary (LGK) tree and a location-guided Steiner (LGS) tree, utilize the geometric locations of the destination nodes as heuristics to compute the trees. They are accompanied by a hybrid location update mechanism to disseminate location information among a group of nodes. Our simulation results show that LGS tree has lower bandwidth cost than LGK tree when the location information of the nodes is up-to-date, and its cost is similar to that of an optimal Steiner multicast tree. When location information of the nodes is out-dated, LGK tree outperforms LGS tree due to its lower computational complexity. <s> BIB014 </s> A survey and comparison on localisation algorithms for wireless ad hoc networks <s> Introduction <s> With advances in wireless networking, devices, applications and middleware, a new area of applications has emerged. Termed mobile commerce, these applications have attracted some interest among researchers, developers, carriers, and content providers. One major issue is the location management support that is needed by many location-intensive mobile commerce applications, such as user and location-specific mobile advertising, mobile inventory management, wireless-business reengineering, and mobile financial services. In this paper, we address the location requirements of m-commerce applications from the user, provider and networking perspectives. We also discuss how such requirements may be supported by the exiting and emerging wireless networks. We also present and discuss several open and interesting research problems. <s> BIB015 </s> A survey and comparison on localisation algorithms for wireless ad hoc networks <s> Introduction <s> Abstract Mobile contexts of use vary a lot, and may even be continuously changing during use. The context is much more than location, but its other elements are still difficult to identify or measure. Location information is becoming an integral part of different mobile devices. Current mobile services can be enhanced with location-aware features, thus providing the user with a smooth transition towards context-aware services. Potential application fields can be found in areas such as travel information, shopping, entertainment, event information and different mobile professions. This paper studies location-aware mobile services from the user's point of view. The paper draws conclusions about key issues related to user needs, based on user interviews, laboratory and field evaluations with users, and expert evaluations of location-aware services. The user needs are presented under five main themes: topical and comprehensive contents, smooth user interaction, personal and user-generated contents, seamless service entities and privacy issues. <s> BIB016 </s> A survey and comparison on localisation algorithms for wireless ad hoc networks <s> Introduction <s> The significance of ubiquitous computing is rapidly growing on a global scale with the current trend towards mobile computing, computer networks, and wireless communication in business and personal use. We combine principals from ubiquitous computing and context-aware applications to create a framework for location-aware applications to global mobile networks. This paper presents the design for a context-aware mobile information system (CAMIS). The system will support users with location-specific information services and applications. The system uses the concept of a non-intrusive Push to deliver information to mobile users using cell-broadcast technology. <s> BIB017 </s> A survey and comparison on localisation algorithms for wireless ad hoc networks <s> Introduction <s> We are developing an acoustic habitat-monitoring sensor network that recognizes and locates specific animal calls in real time. We investigate the system requirements of such a real-time acoustic monitoring network. We propose a system architecture and a set of lightweight collaborative signal processing algorithms that achieve real-time behavior while minimizing inter-node communication to extend the system lifetime. In particular, the target classification is based on spectrogram pattern matching while the target localization is based on beamforming using time difference of arrival (TDOA). We describe our preliminary implementation on a commercial off the shelf (COTS) testbed and present its performance based on testbed measurements. <s> BIB018 </s> A survey and comparison on localisation algorithms for wireless ad hoc networks <s> Introduction <s> Location management is an important part of current and emerging wireless and mobile networks. Location management involves maintaining location information as mobiles power-on, move or power-off. This can be broadly divided into two steps location tracking and location information storage. Location management schemes used in first and second generation wireless networks, such as analogue cellular, PCS and GSM networks, have done a good job of providing a basic location management service for mobile users with limited mobility, applications and battery power under low to moderate traffic conditions in a macro-cellular environment. However, with increased mobility levels, traffic, use of micro and pico-cells, and emerging sophisticated applications, the current location schemes in use may lead to undesirable performance. In this review paper, we address location management issues in detail, present a qualitative analysis of all major location management schemes, discuss performance issues, and discuss several interesting ways to design location management schemes for wireless networks. <s> BIB019 </s> A survey and comparison on localisation algorithms for wireless ad hoc networks <s> Introduction <s> The global positioning system (GPS) is not something that the average person thinks about and how it has affected our civilisation. In many of the systems it is used in, people don't think of it as the primary technology being used for the task at hand. It is a technology that has been taken for granted. Yet, without this technology, many of society's activities would be disrupted in some way. In this paper, the beginnings of GPS are traced while also exploring how it has embedded itself into a wide range of today's products. We will see how companies found new markets for their products with this technology and how this technology has displaced other technologies and practices. We also learn about the firms that found ways to use this technology. What were some of the problems they faced? Were they successful in integrating the technology into their products? Which companies failed to see the value of the technology and how were they affected? <s> BIB020 </s> A survey and comparison on localisation algorithms for wireless ad hoc networks <s> Introduction <s> The recent advances in MEMS, embedded systems and wireless communication technologies are making the realization and deployment of networked wireless microsensors a tangible task. In this paper we study node localization, a component technology that would enhance the effectiveness and capabilities of this new class of networks. The n-hop multilateration primitive presented here, enables ad-hoc deployed sensor nodes to accurately estimate their locations by using known beacon locations that are several hops away and distance measurements to neighboring nodes. To prevent error accumulation in the network, node locations are computed by setting up and solving a global non-linear optimization problem. The solution is presented in two computation models, centralized and a fully distributed approximation of the centralized model. Our simulation results show that using the fully distributed model, resource constrained sensor nodes can collectively solve a large non-linear optimization problem that none of the nodes can solve individually. This approach results in significant savings in computation and communication, that allows fine-grained localization to run on a low cost sensor node we have developed. <s> BIB021 </s> A survey and comparison on localisation algorithms for wireless ad hoc networks <s> Introduction <s> Position information of individual nodes is useful in implementing functions such as routing and querying in ad-hoc networks. Deriving position information by using the capability of the nodes to measure time of arrival (TOA), time difference of arrival (TDOA), angle of arrival (AOA) and signal strength have been used to localize nodes relative to a frame of reference. The nodes in an ad-hoc network can have multiple capabilities and exploiting one or more of the capabilities can improve the quality of positioning. In this paper, we show how AOA capability of the nodes can be used to derive position information. We propose a method for all nodes to determine their orientation and position in an ad-hoc network where only a fraction of the nodes have positioning capabilities, under the assumption that each node has the AOA capability. <s> BIB022 </s> A survey and comparison on localisation algorithms for wireless ad hoc networks <s> Introduction <s> We demonstrate that it is possible to achieve accurate localization and tracking of a target in a randomly placed wireless sensor network composed of inexpensive components of limited accuracy. The crucial enabler for this is a reasonably accurate local coordinate system aligned with the global coordinates. We present an algorithm for creating such a coordinate system without the use of global control, globally accessible beacon signals, or accurate estimates of inter-sensor distances. The coordinate system is robust and automatically adapts to the failure or addition of sensors. Extensive theoretical analysis and simulation results are presented. Two key theoretical results are: there is a critical minimum average neighborhood size of 15 for good accuracy and there is a fundamental limit on the resolution of any coordinate system determined strictly from local communication. Our simulation results show that we can achieve position accuracy to within 20% of the radio range even when there is variation of up to 10% in the signal strength of the radios. The algorithm improves with finer quantizations of inter-sensor distance estimates: with 6 levels of quantization position errors better than 10% are achieved. Finally we show how the algorithm gracefully generalizes to target tracking tasks. <s> BIB023 </s> A survey and comparison on localisation algorithms for wireless ad hoc networks <s> Introduction <s> Position centric approaches, such as Cartesian routing, geographic routing, and the recently proposed trajectory based forwarding (TBF), address scalability issues in large ad hoc networks by using Euclidean space as a complementary name space. These approaches require. that nodes know their position in a common coordinate system. While a GPS receiver in each node would be ideal, in many cases an approximation algorithm is necessary for networks with only a few GPS enabled nodes. These algorithms however require collaboration of large portions of the network, thus imposing an overhead for nodes which do not need positioning, or are mobile. We propose Local Positioning System (LPS), a method that makes use of local node capabilities-angle of arrival, range estimations, compasses and accelerometers, in order to internally position only the groups of nodes involved in particular conversations. Localized positioning enables position centric uses, like discovery, flooding and routing in networks where global positioning is not available. <s> BIB024 </s> A survey and comparison on localisation algorithms for wireless ad hoc networks <s> Introduction <s> Numerous factors contribute to errors in sensor measurements. In order to be useful, any sensor device must be calibrated to adjust its accuracy against the expected measurement scale. In large-scale sensor networks, calibration will be an exceptionally difficult task since sensor nodes are often not easily accessible and manual device-by-device calibration is intractable. In this paper, we present a two-phase post-deployment calibration technique for large-scale, dense sensor deployments. In its first phase, the algorithm derives relative calibration relationships between pairs of co-located sensors, while in the second phase, it maximizes the consistency of the pair-wise calibration functions among groups of sensor nodes. The key idea in the first phase is to use temporal correlation of signals received at neighboring sensors when the signals are highly correlated (i.e. sensors are observing the same phenomenon) to derive the function relating their bias in amplitude. We formulate the second phase as an optimization problem and present an algorithm suitable for localized implementation. We evaluate the performance of the first phase of the algorithm using empirical and simulated data. <s> BIB025 </s> A survey and comparison on localisation algorithms for wireless ad hoc networks <s> Introduction <s> Location management is one of the most important issues of mobile networking systems. Most current mobile systems employ a two-tier database structure to store mobile users' information. HLR (Home Location Register) is used to retrieve user's information, and VLR (Visitor Location Register) is the temporal database for storing visitors' profiles. In the case when the number of users exceeds the capacity of the VLR due to mobility, database overflow occurs. To solve this problem, different replacement policies have been developed: random, most-idle, and inactive. In this paper, we propose a new policy, the least frequent replacement policy, which selects the least frequently accessed users as replacement candidates. Extensive simulation is carried out to predict the performance of the existing replacement policies and the proposed least frequent policy. Our simulation results show that the most idle and least frequent policies outperform the inactive and random replacement policies in most cases and the least frequent policy performs slightly better than the most idle replacement policy. <s> BIB026 </s> A survey and comparison on localisation algorithms for wireless ad hoc networks <s> Introduction <s> A novel task-oriented self-organization algorithm that accounts for mostly location-dependent tasks and heterogeneous sensors inherent in dense ad-hoc sensor systems is proposed. It forms a sensor group for an announced task by sequentially selecting the best matched sensors using a leader election algorithm and a residual task calculation algorithm. To improve the associated communication overhead, the sensor node location information is used in task broadcasting, thus confining the algorithm implementation to a dynamically maintained contributor group which comprises of those sensors which may contribute to the task. Sensor localization is based on a refinement of an algorithm in which utilizes only the neighborhood information of each sensor node corresponding to its each preset radio transmission power level. The proposed self-organization algorithm and how various system parameters affect its performance are examined via extensive simulations. In a densely deployed sensor system, when the refined localization scheme is demonstrated to achieve very good localization, the proposed self-organization algorithm consistently yields a sensor group that covers the announced task. <s> BIB027 </s> A survey and comparison on localisation algorithms for wireless ad hoc networks <s> Introduction <s> Sensor Positioning is a fundamental and crucial issue for sensor network operation and management. In the paper, we first study some situations where most existing sensor positioning methods tend to fail to perform well, an example being when the topology of a sensor network is anisotropic. Then, we explore the idea of using dimensionality reduction techniques to estimate sensors coordinates in two (or three) dimensional space, and we propose a distributed sensor positioning method based on multidimensional scaling technique to deal with these challenging conditions. Multidimensional scaling and coordinate alignment techniques are applied to recover positions of adjacent sensors. The estimated positions of the anchors are compared with their true physical positions and corrected. The positions of other sensors are corrected accordingly. With iterative adjustment, our method can overcome adverse network and terrain conditions, and generate accurate sensor position. We also propose an on demand sensor positioning method based on the above method. <s> BIB028 </s> A survey and comparison on localisation algorithms for wireless ad hoc networks <s> Introduction <s> Embedded networked sensors promise to revolutionize the way we interact with our physical environment and require scalable, ad hoc deployable and energy-efficient node localization/positioning.This paper describes the motivation, design, implementation, and experimental evaluation (on sharply resource-constrained devices) of a self-configuring localization system using radio beacons. We identify beacon density as an important parameter in determining localization quality, which saturates at a transition density. We develop algorithms to improve localization quality by (i) automating placement of new beacons at low densities (HEAP) and (ii) rotating functionality among redundant beacons while increasing system lifetime at high densities (STROBE). <s> BIB029 </s> A survey and comparison on localisation algorithms for wireless ad hoc networks <s> Introduction <s> The growing interest in mobile ad hoc network techniques has resulted in many routing protocol proposals. Scalability issues in ad hoc networks are attracting increasing attention these days. We survey the routing protocols that address scalability. The routing protocols included in the survey fall into three categories: flat routing protocols; hierarchical routing approaches; GPS augmented geographical routing schemes. The article compares the scalability properties and operational features of the protocols and discusses challenges in future routing protocol designs. <s> BIB030 </s> A survey and comparison on localisation algorithms for wireless ad hoc networks <s> Introduction <s> Thank you for reading global positioning system theory and practice. Maybe you have knowledge that, people have search hundreds times for their favorite novels like this global positioning system theory and practice, but end up in infectious downloads. Rather than reading a good book with a cup of coffee in the afternoon, instead they are facing with some malicious bugs inside their desktop computer. global positioning system theory and practice is available in our digital library an online access to it is set as public so you can get it instantly. Our digital library spans in multiple locations, allowing you to get the most less latency time to download any of our books like this one. Merely said, the global positioning system theory and practice is universally compatible with any devices to read. <s> BIB031
An ad hoc wireless network is a self-organized and rapidly deployable network. It usually consists of a large number of unattended nodes that autonomously construct a network and communicate with each other over multi-hop paths. The unattended nature of the system necessitates a set of mechanisms to assure simple deployment while maintaining the self-organized nature. Recently, location-based services have gained considerable attention from academia and industry. Current reported applications and services include coverage analysis BIB007  , location-aware applications  BIB015 BIB011 BIB002 BIB016 BIB017 , environmental monitoring BIB003 BIB008 , target tracking BIB018 BIB012 , battlefield surveillance  , and intrusion detection BIB013 . In addition, location management and efficient routing protocols also require location knowledge BIB026 BIB019 BIB004  BIB014 BIB030 . To obtain the location information, the Global Positioning System (GPS) BIB020 BIB031 could be used. However, it can not be used for in-door applications and is inappropriate for large scale ad hoc networks because of constraints on volume, power consumption, and cost. Alternatively, distributed localization algorithms enable nodes to determine their relative positions automatically after deployment. If absolute positions are necessary, a limited number of nodes (called anchors) must have the capability of determining their absolute positions. Anchors obtain their absolute position using manual configuration or techniques such as GPS. Much localization research has been carried out using this approach BIB027  BIB028 BIB021 . Most of existing algorithms take advantage of mature micro-sensor technology. Time of arrival (TOA) measures the radio signals traveling time, and time difference of arrival (TDOA) measures the time difference of the radio signals arrived at various antennas. These are two common methods for range estimation and have been applied in many infrastructure based systems BIB001 BIB005 and infrastructure free sensor networks BIB009   . Additionally, angle of arrival (AOA) has been proposed to estimate relative angles between neighbors BIB022 . A good survey of these distance measurement systems can be found in   . Still, a different method of measuring the range is through received signal strength indicator (RSSI). RSSI does not require extra equipment and is widely supported by current transceivers. Consequently, RSSI is commonly adopted by many localization systems BIB027 BIB028 BIB006  . Based on the reliance on the hardware support, localization algorithms can be classified into two main categories: range-based algorithms and range-free algorithms. Range-based algorithms rely more on hardware support by applying either one or a combination of TOA, TDOA, AOA, or RSSI technologies. On the contrary, range-free algorithms require less or no hardware support BIB027   BIB023  . Absolute positions are necessary for many applications. But some applications require only the knowledge of nodes' relative position (without actual physical or absolute position information). This means that, at least for some applications, the position information can be relative instead of absolute BIB024 BIB010 . Consequently, the localization algorithms can also be categorized as absolute and relative. To initialize the positioning process, different methods are used by diverse localization algorithms. A common approach for absolute localization algorithms is to let anchors broadcast their position information to the whole network. On the contrary, relative localization algorithms usually have the interested nodes, who want to find an optimal routing path to the destination nodes, to first broadcast the hello packets to their neighbors. Through communication, neighboring nodes can measure the distance between themselves. Based on these distances, all nodes can estimate their relative positions with each other through distributed localization algorithms. In the presence of anchor nodes, absolute positions of all nodes can be derived accordingly. The fraction of anchors within a network and their positions are critical to the precision and performance of localization algorithms. Bulusu et al. BIB029 proposed selfconfiguring nodes into anchors in order to optimize the performance of localization algorithms. The main purpose of the self-configuring is to select the most appropriate nodes that must act as anchors in order to achieve efficient and robust localization for unattended, scalable sensor networks under various system and environment. The method consists of two steps. First, it estimates all nodes' physical positions. Second, it analyzes the local node's density within the network. Based on the nodes' density, Bulusu uses either HEAP or STROBE: for sparse deployments, the HEAP algorithm is used to find candidate positions for additional anchor deployments; and for dense deployments, the STROBE algorithm enables anchors to cooperatively switch on and off, with the aim of less interference and optimal energy conservation. Most localization algorithms assume certain capabilities of the node in the network. Range-based methods use micro-sensors to measure time, relative angle, or energy in order to get range estimation. Range-free methods assume anchor nodes can transmit radios with various power levels or with higher power compared with normal nodes. By default, all algorithms assume the sensors can measure signals without system bias, or at most with random errors that can be minimized by smoothing or averaging. Notice that calibration can be an exceptionally difficult task for large ad hoc networks, Bychkovskiy et al. BIB025 provided a collaborative calibration method for dense networks. The main idea is to minimize, by utilizing redundancy information, the systematic errors by calibrating one sensor's output against the output from others. Though it is a relative calibration method, we believe it can be useful for the distributed localization algorithms considered in this paper. The main contribution of this paper is to present a survey of distributed localization algorithms with a focus on their constraints, advantages, and limits. In addition, we compare and improve a set of representative algorithms. We hope this paper will provide a better understanding of the activities in this research field. The remainder of the paper is organized as follows: In Section 2, we introduce the range-based algorithms. In Section 3, we present range-free algorithms. Section 4 provides relative localization algorithms. Density analysis will be given in Section 5. In Section 6, we present the estimation precision from original research of all algorithms. Section 7 compares a set of representative algorithms under same network environment. Section 8 concludes the report and outlines future research.