J. Caffery

Bio: J. Caffery is an academic researcher from Georgia Institute of Technology. The author has contributed to research in topics: Cellular network & Non-line-of-sight propagation. The author has an hindex of 11, co-authored 12 publications receiving 2552 citations. Previous affiliations of J. Caffery include University of Cincinnati.

Overview of radiolocation in CDMA cellular systems

Abstract: Applications for the location of subscribers of wireless services continue to expand. Consequently, location techniques for wireless technologies are being investigated. With code-division multiple access (CDMA) being deployed by a variety of cellular and PCS providers, developing an approach for location in CDMA networks is imperative. This article discusses the applications of location technology, the methods available for its implementation in CDMA networks, and the problems that are encountered when using CDMA networks for positioning.

Subscriber location in CDMA cellular networks

Abstract: Subscriber radio location techniques are investigated for code-division multiple-access (CDMA) cellular networks. Two methods are considered for radio location: measured times of arrival (ToA) and angles of arrival (AoA). The ToA measurements are obtained from the code tracking loop in the CDMA receiver, and the AoA measurements at a base station (BS) are assumed to be made with an antenna array. The performance of the two methods is evaluated for both ranging and two-dimensional (2-D) location, while varying the propagation conditions and the number of BS's used for the location estimate.

A new approach to the geometry of TOA location

Abstract: Positioning a transmitter via measured times of arrival (TOAs), or range measurements, is a familiar technique that has received much attention in the literature. In the traditional geometric interpretation, TOAs generate circles whose intersections provide the estimate of the transmitter. In this paper a new geometrical interpretation is presented in which straight lines of position (LOPs), rather than the circular LOPs, are used to determine the position of the transmitter. The straight LOPs come from a simple observation regarding the geometry of the system and are not obtained from linearization. Two methods using the straight LOPs are given and their performance is analyzed and compared to methods which employ linearization.

A scattering model based approach to NLOS mitigation in TOA location systems

Abstract: We present a novel approach for reducing the effect of non-line-of-sight (NLOS) error that inhibits accurate location of wireless mobile stations (MSs). The location algorithm is developed based on the distribution of times of arrival (TOAs) generated from multipath scattering models that have been published in the literature. By matching the statistics of the measured TOAs of several multipath arrivals with those produced by the scattering models, estimates of the line-of-sight (LOS) TOAs between each base station (BS) and the MS are obtained. The LOS TOAs can then be used in any traditional TOA location algorithm. The algorithm shows a significant improvement in location accuracy for a TOA system in NLOS environment.

ML and Bayesian TOA location estimators for NLOS environments

Abstract: A major concern of cellular and PCS-based wireless location systems is the effect of the harsh propagation environment, particularly non-line-of-sight (NLOS) propagation. In order to improve location accuracy under such conditions, this paper proposes a novel location technique that estimates the true, or line-of-sight (LOS), ranges based on NLOS range measurements. The algorithms, designed for NLOS environments, make use of well-known multipath scattering models (ring/disk of scatterers and Gaussian distributed scatterers) in order to incorporate the effects of NLOS propagation. From PDFs of the TOAs derived using the models, maximum likelihood expectation-maximization and Bayesian estimators are applied to multipath TOA measurements at each BS to estimate the LOS distance between the MS and the BS. Simulated results show that the algorithms provide considerable improvement over traditional location algorithms.

Survey of Wireless Indoor Positioning Techniques and Systems

Abstract: Wireless indoor positioning systems have become very popular in recent years. These systems have been successfully used in many applications such as asset tracking and inventory management. This paper provides an overview of the existing wireless indoor positioning solutions and attempts to classify different techniques and systems. Three typical location estimation schemes of triangulation, scene analysis, and proximity are analyzed. We also discuss location fingerprinting in detail since it is used in most current system or solutions. We then examine a set of properties by which location systems are evaluated, and apply this evaluation method to survey a number of existing systems. Comprehensive performance comparisons including accuracy, precision, complexity, scalability, robustness, and cost are presented.

On the capacity of a cellular CDMA system

Abstract: It is shown that, particularly for terrestrial cellular telephony, the interference-suppression feature of CDMA (code division multiple access) can result in a many-fold increase in capacity over analog and even over competing digital techniques. A single-cell system, such as a hubbed satellite network, is addressed, and the basic expression for capacity is developed. The corresponding expressions for a multiple-cell system are derived. and the distribution on the number of users supportable per cell is determined. It is concluded that properly augmented and power-controlled multiple-cell CDMA promises a quantum increase in current cellular capacity. >

Dynamic fine-grained localization in Ad-Hoc networks of sensors

Abstract: The recent advances in radio and em beddedsystem technologies have enabled the proliferation of wireless microsensor networks. Such wirelessly connected sensors are released in many diverse environments to perform various monitoring tasks. In many such tasks, location awareness is inherently one of the most essential system parameters. It is not only needed to report the origins of events, but also to assist group querying of sensors, routing, and to answer questions on the network coverage. In this paper we present a novel approach to the localization of sensors in an ad-hoc network. We describe a system called AHLoS (Ad-Hoc Localization System) that enables sensor nodes to discover their locations using a set distributed iterative algorithms. The operation of AHLoS is demonstrated with an accuracy of a few centimeters using our prototype testbed while scalability and performance are studied through simulation.

Range-Free Localization Schemes for Large Scale Sensor Networks 1

Abstract: Sensor Networks have been proposed for a multitude of location-dependent applications. For such systems, the cost and limitations of the hardware on sensing nodes prevent the use of range-based localization schemes that depend on absolute point- to-point distance estimates. Because coarse accuracy is sufficient for most sensor network applications, solutions in range-free localization are being pursued as a cost-effective alternative to more expensive range-based approaches. In this paper, we present APIT, a novel localization algorithm that is range-free. We show that our APIT scheme performs best when an irregular radio pattern and random node placement are considered, and low communication overhead is desired. We compare our work via extensive simulation, with three state-of-the-art range-free localization schemes to identify the preferable system configurations of each. In addition, we study the effect of location error on routing and tracking performance. We show that routing performance and tracking accuracy are not significantly affected by localization error when the error is less than 0.4 times the communication radio radius.

Range-free localization schemes for large scale sensor networks

Abstract: Wireless Sensor Networks have been proposed for a multitude of location-dependent applications. For such systems, the cost and limitations of the hardware on sensing nodes prevent the use of range-based localization schemes that depend on absolute point-to-point distance estimates. Because coarse accuracy is sufficient for most sensor network applications, solutions in range-free localization are being pursued as a cost-effective alternative to more expensive range-based approaches. In this paper, we present APIT, a novel localization algorithm that is range-free. We show that our APIT scheme performs best when an irregular radio pattern and random node placement are considered, and low communication overhead is desired. We compare our work via extensive simulation, with three state-of-the-art range-free localization schemes to identify the preferable system configurations of each. In addition, we study the effect of location error on routing and tracking performance. We show that routing performance and tracking accuracy are not significantly affected by localization error when the error is less than 0.4 times the communication radio radius.