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.

Survey of Wireless Indoor Positioning Techniques and Systems

In previous years, positioning systems for indoor areas using the existing wireless local area network infrastructure have been suggested. Such systems make use of location fingerprinting rather than time or direction of arrival techniques for determining the location of mobile stations. While experimental results related to such positioning systems have been presented, there is a lack of analytical models that can be used as a framework for designing and deploying the positioning systems. In this paper, we present an analytical model for analyzing such positioning systems. We develop the framework for analyzing a simple positioning system that employs the Euclidean distance between a sample signal vector and the location fingerprints of an area stored in a database. We analyze the effect of the number of access points that are visible and radio propagation parameters on the performance of the positioning system and provide some preliminary guidelines on its design.

Modeling of indoor positioning systems based on location fingerprinting

Wireless positioning has attracted much research attention and has become increasingly important in recent years. Wireless positioning has been found very useful for other applications besides E911 service, ranging from vehicle navigation and network optimization to resource management and automated billing. Although many positioning devices and services are currently available, it is necessary to develop an integrated and seamless positioning platform to provide a uniform solution for different network configurations. This article surveys the state-of-the-art positioning designs, focusing specifically on signal processing techniques in network-aided positioning. It serves as a tutorial for researchers and engineers interested in this rapidly growing field. It also provides new directions for future research for those who have been working in this field for many years.

Signal processing techniques in network-aided positioning: a survey of state-of-the-art positioning designs

The term “location fingerprinting” covers a wide variety of methods for determining receiver position using databases of radio signal strength measurements from different sources. In this work we present a survey of location fingerprinting methods, including deterministic and probabilistic methods for static estimation, as well as filtering methods based on Bayesian filter and Kalman filter. We present a unified mathematical formulation of radio map database and location estimation, point out the equivalence of some methods from the literature, and present some new variants. A set of tests in an indoor positioning scenario using WLAN signal strengths is performed to determine the influence of different calibration and location method parameters. In the tests, the probabilistic method with the kernel function approximation of signal strength histograms was the best static positioning method. Moreover, all filters improved the results significantly over the static methods.

A comparative survey of WLAN location fingerprinting methods

Indoor environments present opportunities for a rich set of location-aware applications such as navigation tools for humans and robots, interactive virtual games, resource discovery, asset tracking, location-aware sensor networking etc Typical indoor applications require better accuracy than what current outdoor location systems provide Outdoor location technologies such as GPS have poor indoor performance because of the harsh nature of indoor environments Further, typical indoor applications require different types of location information such as physical space, position and orientation 
This dissertation describes the design and implementation of the Cricket indoor location system that provides accurate location in the form of user space, position and orientation to mobile and sensor network applications 
Cricket consists of location beacons that are attached to the ceiling of a building, and receivers, called listeners, attached to devices that need location Each beacon periodically transmits its location information in an RF message At the same time, the beacon also transmits an ultrasonic pulse The listeners listen to beacon transmissions and measure distances to nearby beacons, and use these distances to compute their own locations This active-beacon passive-listener architecture is scalable with respect to the number of users, and enables applications that preserve user privacy 
This dissertation describes how Cricket achieves accurate distance measurements between beacons and listeners Once the beacons are deployed, the MAT and AFL algorithms, described in this dissertation, use measurements taken at a mobile listener to configure the beacons with a coordinate assignment that reflects the beacon layout This dissertation presents beacon interference avoidance and detection algorithms, as well as outlier rejection algorithms to prevent and filter out outlier distance estimates caused by uncoordinated beacon transmissions 
The Cricket listeners can measure distances with an accuracy of 5 cm The listeners can detect boundaries with an accuracy of 1 cm Cricket has a position estimation accuracy of 10 cm and an orientation accuracy of 3 degrees (Copies available exclusively from MIT Libraries, Rm 14-0551, Cambridge, MA 02139-4307 Ph 617-253-5668; Fax 617-253-1690)

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The cricket indoor location system

Wireless LANs are becoming increasingly popular today, particularly those based on IEEE 802.11b standard. We study the problem of determining the location of a mobile device, which is communicating through a WLAN. We exploit the fact that the strength of the signals that a device will receive from different access points will vary with location. We build a database of signal strength information for various locations, and use this information to determine which location a given test data comes from. The problem is complicated because RF signals are affected by the noise, interference, multi-path effect, and random movement in the environment. We find that in spite of this randomness, the signal information is sufficient to detect the position of mobile device with certain error margin.

K. Chaudhuri

Papers

Location determination of a mobile device using IEEE 802.11b access point signals