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A.K. Othman GPS-less Localization Protocol for Underwater Acoustic Networks
Abstract
The problem of underwater positioning is increasingly crucial due to the emerging importance of sub-sea activities. Knowledge of node location is essential for many applications for which sensor networks can be used. At the surface, positioning problems have been resolved by the extended use of GPS, which is straightforward and effective. Unfortunately, using GPS in the sub-sea environment is impossible and positioning requires the use of special systems. One of the major challenges in the underwater acoustic networks (UANs) area of research is the development of a networking protocol that can cope with the management of a dynamic sub-sea network. We propose a scheme to perform node discovery, using only one seed node (primary seed) in a known position. The discovery protocol can be divided into two parts: First, building up the relative co-ordinate system. Second, involving more remote nodes becoming seed nodes for further discoveries. Four different algorithms have been investigated; (i) Farthest/Farthest Algorithm, (ii) Farthest/Nearest Algorithm, (iii) Nearest/Farthest Algorithm and (iv) Nearest/Nearest Algorithm. We investigated the performances of random and fixed (grid) network topologies. Different locations of primary seed node were exercised and statistics for node discovery will be reported.
... Localization and (eventually) mapping are key to successful navigation in autonomous mobile platform technology, and are fundamental tasks performed in order to achieve high levels of autonomy in robot navigation, and robustness in vehicle positioning and values of the data [45], [46], [47], [48], [49], [50], [51], [52], [53]. In the case of a swarm, we can use cooperative localization as in [54], [55]. ...
The subject is the localization problem of an underwater swarm of autonomous underwater robots (AUV), in the frame of the HARNESS project; by localization, we mean the relative swarm configuration, i.e., the geometrical shape of the group. The result is achieved by using the signals that the robots exchange. The swarm is organized by rules and conceived to perform tasks, ranging from environmental monitoring to terrorism-attack surveillance. Two methods of determining the shape of the swarm, both based on trilateration calculation, are proposed. The first method focuses on the robot's speed. In this case, we use our knowledge of the speeds and distances between the machines, while the second method considers only distances and the orientation angles of the robots. Unlike a trilateration problem, we do not know the position of the beacons and this renders the problem a difficult one. Moreover, we have very few data. More than one step of motion is needed to resolve the multiple solutions found, owing to the symmetries of the system and optimization process of one or more objective functions leading to the final configuration. We subsequently checked our algorithm using a simulator taking into account random errors affecting the measurements
... Acoustic energy propagates quite well in the sea, and hence acoustic transponders can be used as beacons to guide the motion of an AUV under the water without emersion. [24] The most commonly used way to obtain position information underwater is through the use of underwater acoustic networks (UAV). These net are at known positions and the AUV obtains the range and/or bearing to several of these and then calculates its position through trilateration (intersection of spherical surfaces) or triangulation (locations of points by angle measurements). ...
... Localization and (eventually) mapping are key to successful navigation in autonomous mobile platform technology, and are fundamental tasks performed in order to achieve high levels of autonomy in robot navigation, and robustness in vehicle positioning and values of the data [45, 46, 47,48,49,50,51,52,53]. In the case of a swarm, we can use cooperative localization as in [54,55]. ...
This paper is the extension of work presented at the IARP Conference "Bio inspired robotics" held in Frascati (Italy), 14 May 2014.
The subject is the localization problem of an underwater swarm of autonomous underwater robots (AUV), in the frame of the HARNESS project; by localization, we mean the relative swarm configuration, i.e., the geometrical shape of the group. The result is achieved by using the signals that the robots exchange. The swarm is organized by rules and conceived to perform tasks, ranging from environmental monitoring to terrorism-attack surveillance.
Two methods of determining the shape of the swarm, both based on trilateration calculation, are proposed. The first method focuses on the robot's speed. In this case, we use our knowledge of the speeds and distances between the machines, while the second method considers only distances and the orientation angles of the robots. Unlike a trilateration problem, we do not know the position of the beacons and this renders the problem a difficult one. Moreover, we have very few data. More than one step of motion is needed to resolve the multiple solutions found, owing to the symmetries of the system and optimization process of one or more objective functions leading to the final configuration. We subsequently checked our algorithm using a simulator taking into account random errors affecting the measurements.
... Othman et al. proposed a node discovery and localization protocol (NDLP) for UASNs [9] [10]; it is an anchor-free and range-based localization method. Localization begins with a node discovery phase by a seed node, which is aware of its self-position and selects other seeds iteratively. ...
Recently underwater acoustic sensor networks (UASNs) have drawn much attention because of their great value in many underwater applications where human operation is hard to carry out. In this paper, we introduce and compare the performance of four localization algorithms in UASNs, namely, distance vector-hop (DV-hop), a new localization algorithm for underwater acoustic sensor networks (NLA), large-scale
hierarchical localization (LSHL), and localization scheme for large scale underwater networks (LSLS). The four algorithms are all suitable for large-scale UASNs. We compare the localization algorithms in terms of localization coverage, localization error, and average energy consumption. Besides, we analyze the impacts of the ranging error and the number of anchor nodes on the performance of the localization algorithms. Simulations
show that LSHL and LSLS perform much better than DV-hop and NLA in localization coverage, localization error, and average energy consumption. The performance of NLA is similar to that of the DV-hop. The advantage of DV-hop and NLA is that the localization results do not rely on the number of anchor nodes; that is, only a small number of anchor nodes are needed for localization.
... To determine an accurate estimate of the location of an unknown node it is essential to have the clocks of the sensor nodes synchronized. Nevertheless, when designing underwater range-based localization algorithms often times nodes are assumed to be time synchronized [8], [9], [10], and/or clock skews are not taken into consideration [11]. Very limited research works have addressed joint localization and time synchronization for UW-ASNs. ...
... To determine an accurate estimate of the location of an unknown node it is essential to have the clocks of the sensor nodes synchronized. Nevertheless, when designing underwater range-based localization algorithms often times nodes are assumed to be time synchronized [9], [10], [11], and/or clock skews are not taken into consideration [12]. ...
Localization and time synchronization are both essential services for Internet-connected underwater acoustic testbeds. Although the two are mutually coupled, they are often treated separately. We propose a new low-cost distributed networked localization and time synchronization framework for underwater acoustic sensor network testbeds. The proposal is based on decoupling the two problems and solving first the time synchronization then localization using the same set of messages, i.e. with no additional overhead. A coarse, followed by a fine-grained localization algorithms are adopted to accurately estimate the location of an unknown node. The protocol is robust to noisy range measurements. The proposed scheme is implemented in a testbed based on Teledyne Benthos Telesonar SM-975 underwater modems and tested extensively in Lake LaSalle at the University at Buffalo. Experiments and simulations in terms of root mean square error (RMSE) demonstrate that the proposed scheme can achieve a high accuracy for a given energy budget, i.e. for a given number of message exchanges. I. INTRODUCTION Localization in underwater acoustic (UW-A) networks is essential for geographical routing, medium access control (MAC), autonomous underwater vehicle (AUV) navigation, IP connectivity [1], among other applications. One way to perform localization is to rely on GPS. However, radio waves are highly attenuated underwater. Acoustic communication is the transmission technology of choice for underwater networked systems [2]. The UW-A channel is characterized by slow propagation of acoustic waves, limited bandwidth, high transmit energy consumption, high and variable propagation delays, motion-induced Doppler spread, frequency selective fading and multipath [3], [4]. These characteristics pose severe challenges towards designing robust localization schemes that can achieve the following desirable properties: i) high accuracy, ii) fast convergence, iii) wide coverage, iv) low communication cost, and v) high scalability. Localization in general requires several sensor nodes with known locations (anchor nodes) with the distance or angle measurements between the anchor nodes and the unknown node. In wireless sensor networks (WSNs) distance or angle can be measured using one of the following methods: i) Angle-of-Arrival (AoA), ii) Received Signal Strength Indicator (RSSI), iii) Time-of-Arrival (ToA), and iv) Time Difference of Arrival (TDoA). In underwater acoustic sensor networks (UW-ASNs) ToA and TDoA are more widely used, as RSSI suffer due to the time varying nature of the UW-A channel and AoA requires an array of transducers, which can be very costly to provide in underwater sensor network deployments [5]. A number of localization techniques have been proposed for UW-ASNs [6], [7], [8], which can be categorized into centralized and decentralized; each can be further sub-categorized into estimation-based and prediction-based. In general, centralized localization schemes rely on a central controller, while decentralized schemes can perform localization autonomously. To determine an accurate estimate of the location of an unknown node it is essential to have the clocks of the sensor nodes synchronized. Nevertheless, when designing underwater range-based localization algorithms often times nodes are assumed to be time synchronized [9], [10], [11], [12], and/or clock skews are not taken into consideration [13]. Very limited research only has addressed joint localization and time synchronization for UW-ASNs. Among them in [12], JSL, a joint time synchronization and localization protocol with stratification and mobility compensation is presented. However, JSL does not consider range measurement errors and it makes use of a linear least squares quadratic linearization algorithm for localization, which is known to suffer when anchor node location and/or propagation time estimate is not precise [14]. Moreover, to compensate for the stratification effect it assumes the sound speed profile is known a-priori. In [15], a heuristic algorithm for time synchronization and localization in the UW-A channel is presented. The algorithm relies on the assumption that nodes are equipped with self-navigation systems and that they provide accurate information, which might not be realistic, as the accuracy of such a system can have a strong impact on the localization algorithm. It is still desirable to have a robust autonomous networked infrastructure that can provide both localization and time synchronization services at low-cost in practical testbed deployments. To fill that gap, we therefore propose a low-cost distributed networked localization and time synchronization framework for UW-ASNs. The proposal is based on the Internet underwater framework [1], recently proposed and implemented by our research group at the University at Buffalo. The proposed time synchronization and localization algorithms are implemented in a testbed based on Teledyne Benthos Telesonar SM-975 underwater modems and tested extensively in Lake LaSalle at the University at Buffalo. Experiments in terms of root mean square error (RMSE) demonstrate that the proposed scheme can achieve a high accuracy for a given energy budget. The rest of this paper is organized as follows. In Section II, we introduce the problem statement followed by time synchronization and localization algorithms. In Section III, we describe the UW-Buffalo testbed architecture. In Section IV, we evaluate the proposed scheme. Finally, in Section V, we draw the main conclusions.
This article considers the joint problem of packet scheduling and
self-localization in an underwater acoustic sensor network where sensor nodes
are distributed randomly in an operating area. In terms of packet scheduling,
our goal is to minimize the localization time, and to do so we consider two
packet transmission schemes, namely a collision-free scheme (CFS), and a
collision-tolerant scheme (CTS). The required localization time is formulated
for these schemes, and through analytical results and numerical examples their
performances are shown to be generally comparable. However, when the packet
duration is short (as is the case for a localization packet), and the operating
area is large (above 3km in at least one dimension), the collision-tolerant
scheme requires a smaller localization time than the collision-free scheme.
After gathering enough measurements, an iterative Gauss-Newton algorithm is
employed by each sensor node for self-localization, and the Cramer Rao lower
bound is evaluated as a benchmark. Although CTS consumes more energy for packet
transmission, it provides a better localization accuracy. Additionally, in this
scheme the anchor nodes work independently of each other, and can operate
asynchronously which leads to a simplified implementation.
Underwater Wireless Sensor Networks (UWSNs) are expected to support a variety of civilian and military applications. Sensed data can only be interpreted meaningfully when referenced to the location of the sensor, making localization an important problem. While global positioning system (GPS) receivers are commonly used in terrestrial WSNs to achieve this, this is infeasible in UWSNs as GPS signals do not propagate through water. Acoustic communications is the most promising mode of communication underwater. However, underwater acoustic channels are characterized by harsh physical layer conditions with low bandwidth, high propagation delay and high bit error rate. Moreover, the variable speed of sound and the non-negligible node mobility due to water currents pose a unique set of challenges for localization in UWSNs. In this paper, we provide a survey of techniques and challenges in localization specifically for UWSNs. We categorize them into (i) range-based vs. range-free techniques; (ii) techniques that rely on static reference nodes vs. those who also rely on mobile reference nodes, and (iii) single-stage vs. multi-stage schemes. We compare the schemes in terms of localization speed, accuracy, coverage and communication costs. Finally, we provide an outlook on the challenges that should be, but have yet been, addressed.
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.
In Underwater Wireless Sensor Networks (UWSNs), localization is one of most important technologies since it plays a critical role in many applications. Motivated by widespread adoption of localization, in this paper, we present a comprehensive survey of localization algorithms. First, we classify localization algorithms into three categories based on sensor nodes’ mobility: stationary localization algorithms, mobile localization algorithms and hybrid localization algorithms. Moreover, we compare the localization algorithms in detail and analyze future research directions of localization algorithms in UWSNs.
The maritime domain continues to be important for our society. Significant investments continue to be made to increase our knowledge about what "happens" underwater, whether at or near the sea surface, within the water column, or at the seabed. The latest geophysical, archaeological, and oceanographical surveys deliver more accurate global knowledge at increased resolutions. Surveillance applications allow dynamic systems to be accurately characterized. Underwater exploration is fundamentally reliant on the effective processing of sensor signal data.
All maritime applications face the same difficult operating environment: fading channels, rapidly changing environmental conditions, high noise levels at sensors, sparse coverage of the measurement area, limited reliability of communication channels, and the need for robustness and low energy consumption, just to name a few. There are obvious technical similarities in the signal processing that have been applied to different measurement equipment, and this special issue aims to help foster cross-fertilization between these different application areas.
The articles in this special issue cover the following topics: First, underwater acoustics: "Underwater broadband source localization based on modal filtering and features extraction", "Simulation of matched field processing localization based on EMD denoising and Karhunen-Loève expansion in underwater waveguide environment," "A relative-localization algorithm using incomplete pair-wise distance measurements for underwater applications," "Acoustic particle detection with the ANTARES detector," "Masking of time-frequency patterns in applications of passive underwater target detection," "An underwater acoustic implementation of DFT-spread OFDM," "Low complexity iterative receiver design for shallow water acoustic channels," and "Automatic indexing and content analysis of whale recordings and XML representation."
Second, underwater nonacoustics: "Silent localization of underwater sensors using magnetometers", "Hausdorff-based RC and IESIL combined positioning algorithm for underwater geomagnetic navigation", and "Realistic subsurface anomaly discrimination using electromagnetic induction and an SVM classifier".
Third, radar: "CFAR detection from non-coherent radar echoes using bayesian theory", "Artificial neural network-based clutter reduction systems for ship size estimation in maritime radars."
Fourth, optics: "An evaluation of pixel-based methods for the detection of floating objects on the sea surface," "Statistical real-time model for performance prediction of ship detection from micro-satellite electro-optical imagers," "Techniques for effective optical noise rejection in amplitude-modulated laser optical radars for underwater three-dimensional imaging," "Underwater image processing: state of the art of restoration and image enhancement methods," and "A fully automated method to detect and segment a manufactured object in an underwater color image."
The task of localizing underwater assets involves the relative localization of each unit using only pairwise distance measurements, usually obtained from time-of-arrival or time-delay-of-arrival measurements. In the fluctuating underwater environment, a complete set of pair-wise distance measurements can often be difficult to acquire, thus hindering a straightforward closed-form solution in deriving the assets' relative coordinates. An iterative multidimensional scaling approach is presented based upon a weighted-majorization algorithm that tolerates missing or inaccurate distance measurements. Substantial modifications are proposed to optimize the algorithm, while the effects of refractive propagation paths are considered. A parametric study of the algorithm based upon simulation results is shown. An acoustic field-trial was then carried out, presenting field measurements to highlight the practical implementation of this algorithm.
The design of a suitable interconnection network for inter-processor communication is one of the key issues of the system performance. The reliability of these networks and their ability to continue operating despite failures are major concerns in determining the overall system performance. In this paper a new irregular network IABN has been proposed modifying existing ABN network. ABN is a regular multipath network with limited fault tolerance. The reliabilities of the IABN and ABN multi-stage interconnection networks have been calculated and compared in terms of the Upper and Lower bounds of Mean time to failure (MTTF).The IABN is a network that provides much better fault-tolerance by providing three time more paths between any pair of source-destination and better reliability at the expanse of little more cost than ABN.
Our HiBall Tracking System generates over 2000 head-pose estimates per second with less than one millisecond of latency, and less than 0.5 millimeters and 0.02 degrees of position and orientation noise, everywhere in a 4.5 by 8.5 meter room. The system is remarkably responsive and robust, enabling VR applications and experiments that previously would have been difficult or even impossible.Previously we published descriptions of only the Kalman filter-based software approach that we call Single-Constraint-at-a-Time tracking. In this paper we describe the complete tracking system, including the novel optical, mechanical, electrical, and algorithmic aspects that enable the unparalleled performance.
sent out by a central facility that addresses a particular receiver unit (beeper) and produces an audible signal. In addition, it may display a number to which the called-party should phone back (some systems allow a vocal message to be conveyed about the call-back number). It is then up to the recipient to use the conventional telephone system to call-back confirming the signal and determine the required action. Although useful in practice there are still circumstances where it is not ideal. For instance, if the called party does not reply the controller has no idea if they: 1) are in an area where the signal does not penetrate 2) have been completely out of the area for some time 3) have been too busy to reply or 4) have misheard or misread the call-back number. Moreover, in the case where there are a number of people who could respond to a crisis situation, it is not known which one is the nearest to the crisis and therefore the most suitable to contact. A `tagging system' does not
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).
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.
A method for estimating unknown node positions in a sensor network
based exclusively on connectivity-induced constraints is described.
Known peer-to-peer communication in the network is modeled as a set of
geometric constraints on the node positions. The global solution of a
feasibility problem for these constraints yields estimates for the
unknown positions of the nodes in the network. Providing that the
constraints are tight enough, simulation illustrates that this estimate
becomes close to the actual node positions. Additionally, a method for
placing rectangular bounds around the possible positions for all unknown
nodes in the network is given. The area of the bounding rectangles
decreases as additional or tighter constraints are included in the
problem. Specific models are suggested and simulated for isotropic and
directional communication, representative of broadcast-based and optical
transmission respectively, though the methods presented are not limited
to these simple cases
. This paper addresses the problem of planning the motion of one or more pursuers in a polygonal environment to eventually "see" an evader that is unpredictable, has unknown initial position, and is capable of moving arbitrarily fast. This problem was first introduced by Suzuki and Yamashita. Our study of this problem is motivated in part by robotics applications, such as surveillance with a mobile robot equipped with a camera that must find a moving target in a cluttered workspace. A few bounds are introduced, and a complete algorithm is presented for computing a successful motion strategy for a single pursuer. For simplyconnected free spaces, it is shown that the minimum number of pursuers required is Theta(lg n). For multiply-connected free spaces, the bound is Theta( p h + lg n) pursuers for a polygon that has n edges and h holes. A set of problems that are solvable by a single pursuer and require a linear number of recontaminations is shown. The complete algorithm searches a f...
In this paper, 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 distance 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 networks.
In a surprising result, Korupolu, Plaxton, and Rajaraman (13) showed that a simple local search heuristic for the capacitated facility location problem (CFLP) in which the service costs obey the triangle inequality produces a solution in polynomial time which is within a factor of 8+ ǫ of the value of an optimal solution. By simplifying their analysis, we are able to show that the same heuristic produces a solution which is within a factor of 6(1 + ǫ) of the value of an optimal solution. Our simplified analysis uses the supermodularity of the cost function of the problem and the integrality of the transshipment polyhedron. Additionally, we consider the variant of the CFLP in which one may open multiple copies of any facility. Using ideas from the analysis of the local search heuristic, we show how to turn any α-approximation algorithm for this variant into one which, at an additional cost of twice the optimum of the standard CFLP, opens at most one additional copy of any facility. This allows us to transform a recent 3-approximation algorithm of Chudak and Shmoys (7) that opens many additional copies of facilities into a polynomial-time algorithm which only opens one additional copy and has cost no more than five times the value of the standard CFLP.
In this paper, we address two problems associated with static ad hoc wireless networks; methods of saving energy during a deployment of the nodes, and efficient methods of performing adjacent neighbor discovery. To meet these goals we introduce a family of "birthday protocols"which use random independent transmissions to discover adjacent nodes. Various modes of the birthday protocol are used to solve the two problems. We provide a mathematical model and analysis of two modes of the protocol and are led to a third mode which is the probabilistic analog of the deterministic round robin scheduling algorithm. We show by analysis and simulation that the birthday protocols are a promising tool for saving energy during the deployment of an ad hoc network as well as an efficient and flexible means of having the nodes discover their neighbors
Proximity awareness in Bluetooth technology is implemented via an asymmetric point to point “sender-receiver” protocol where “senders” are trying to discover “receivers” in the vicinity. This paper tries to shed some light on the link formation delay by first identifying the delay bottlenecks in the asymmetric neighborhood discovery process and then discussing the factors that affect certain parameter decisions. A symmetric technique for establishing ad hoc connectivity is introduced which imposes each node to alternate between the “sender” and “receiver” state in a random fashion. The results show that the connection establishment delay can be reduced if appropriate decisions are made in the choice of parameters
Our position location technique provides location information within milliseconds and is integrated in a handheld, direct sequence spread spectrum (DSSS), communications system. We use a standard DSSS waveform, with a state-of-the-art chipping rate to provide a position location capability to an accuracy of less than one meter in a severe multipath environment. We use a two-way time-of-arrival (TOA) measurement technique (with 1 ppm clocks) that eliminates the need to synchronize master and reference radio clocks. Several techniques improve TOA and therefore range accuracy. A loop back calibrates internal system delay. Frequency diversity orthogonalizes multipath with respect to direct path and leading edge curve fitting of the direct path reduces the effect of multipath. Applications include location of urban warfighters, firefighters, police, and medical personnel and resources
Configuration of the computing and communications systems found at
home and in the workplace is a complex task that currently requires the
attention of the user. Researchers have begun to examine computers that
would autonomously change their functionality based on observations of
who or what was around them. By determining their context, using input
from sensor systems distributed throughout the environment, computing
devices could personalize themselves to their current user, adapt their
behaviour according to their location, or react to their surroundings.
The authors present a novel sensor system, suitable for large-scale
deployment in indoor environments, which allows the locations of people
and equipment to be accurately determined. We also describe some of the
context-aware applications that might make use of this fine-grained
location information
In a high-capacity mobile telephone system using cellular technology, a mobile location technique which determines the radio zone in which a moving vehicle exists is one of the most important techniques for the system control. A mobile location technique using a signal strength measurement scheme is described. The probability that a mobile is judged to exist in a certain zone (zone selection rate) is first defined. Dependency of this rate on land mobile propagation characteristics is then discussed in detail. A field test for the justification of this location technique was carried out in the Tokyo metropolitan area in which the field test results agreed well with the estimated values.
A method of vehicle location is discussed in which the attenuation of the signal from a mobile transmitter is measured. A test system and procedure for obtaining data is described. A series of curves are developed which specify the anticipated error for a four-station grid. The signal strength measurements could be very tedious and time consuming, but a system was devised that makes it possible to automate the procedure. This system, called the signal amplitude sampler and totalization unit (SASTU), is fully described.
Despite extraordinary advances in Global Positioning System (GPS)
technology, millions of square meters of indoor space are out of reach
of Navstar satellites. Their signals, originating high above the Earth,
are not designed to penetrate most construction materials, and no amount
of technical wizardry is likely to help. So the greater part of the
world's commerce, being conducted indoors, cannot be followed by GPS
satellites. Here, the authors describe how tracking people and assets
indoors has now moved from the realm of science fiction to reality,
thanks to a radiofrequency identification technique now being introduced
to the market
A Bluetooth ad hoc network can be formed by interconnecting piconets into scatternets. The constraints and properties of Bluetooth scatternets present special challenges in forming an ad hoc network e#ciently. In this paper, we evaluate the performance of a new randomized distributed Bluetooth scatternet formation protocol. Our simulations validate the theoretical results that our scatternet formation protocol runs in O(log n) time and sends O(n) messages. The scatternets formed have the following properties: 1) any device is a member of at most two piconets, and 2) the number of piconets is close to be optimal. These properties can avoid overloading of any single device and lead to low interference between piconets. In addition, the simulations show that the scatternets formed have O(log n) diameter. As an essential part of the scatternet formation protocol, we study the problem of device discovery: establishing multiple connections with many masters and slaves in parallel. We investigate the collision rate and time requirement of the inquiry and page processes. Deducing from the simulations results of scatternet formation and device discovery, we can verify that the total number of packets sent is O(n) and demonstrate that the maximum number of packets sent by any single device is O(log n). At last, we give estimates of the total time requirement of the protocol and suggest further improvements. Keywords Bluetooth, Ad Hoc Networks, Resource Discovery, Topology Construction # This work is supported in part by the MIT Auto-ID Center 1.
This paper presents the design, implementation, and evaluation of Cricket, a location-support system for in-building, mobile, locationdependent 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. 1
We introduce a geographical adaptive delity (GAF) algorithm that reduces energy consumption in ad hoc wireless networks. GAF conserves energy by identifying nodes that are equivalent from a routing perspective and then turning o unnecessary nodes, keeping a constant level of routing delity. GAF moderates this policy using application- and system-level information; nodes that source or sink data remain on and intermediate nodes monitor and balance energy use. GAF is independent of the underlying ad hoc routing protocol; we simulate GAF over unmodied AODV and DSR. Analysis and simulation studies of GAF show that it can consume 40% to 60% less energy than an unmodi ed ad hoc routing protocol. Moreover, simulations of GAF suggest that network lifetime increases proportionally to node density; in one example, a four-fold increase in node density leads to network lifetime increase for 3 to 6 times (depending on the mobility pattern). More generally, GAF is an example of adaptive delity, a technique proposed for extending the lifetime of self-conguring systems by exploiting redundancy to conserve energy while maintaining application delity. 1.
The cricket Location-Support SystemThe Active Badge location System
- N B Priynatha
- A Chakraborty
- H Balakrisnan
- R Want
- A Hopper
- V Falcao
- J Gibbsons
N. B. Priynatha, A. Chakraborty, and H. Balakrisnan, "The cricket Location-Support System," in 6 th ACM International Conference on Mobile Computing and Networking (ACM MOBICOM), August 2000. [17] R. Want, A. Hopper, V. Falcao, and J. Gibbsons, "The Active Badge location System," ACM Transactions on Information System 10, pp. 91-102, January 1992.