Journal of Global Positioning Systems (2004) Vol. 3, No. 1-2: 2-11 GNSS Indoor Location Technologies Gérard Lachapelle Position, Location And Navigation Group, Department of Geomatics Engineering, University of Calgary, Canada Tel: 403 220 7104 E-mail: Lachapelle@geomatics.ucalgary.ca Received: 15 November 2004 / Accepted: 3 February 2005 Abstract. This paper presents an overview of GNSS- based indoor location technologies. Current and emerging users and their potential requirements are first discussed. Signal attenuation and multipath caused under indoor environments are described. The basic method to acquire and track attenuated signals, namely longer integration of signal measurements, is summarized. The need for assisted GPS is addressed. Availability and accuracy performance currently achievable under various conditions (wooden structure building, single family residence, large sport facility) are illustrated through selected test results. The limitations of current technologies and potential enhancements are discussed. These include measurement noise, existing signal structure and future enhancements, frequency and time errors, user motion, sensor aiding such as ultra-tight integration, and solution reliability and continuity. The paper concludes with a discussion of receiver testing standards. The possibility of using a GNSS hardware simulator to create reproducible indoor environments in order to overcome the controllability issue encountered with real environments is analysed. Key words: Indoor location, AGPS, HSGPS, aided GPS, Indoor GPS 1 Introduction The need for indoor location was initially spurred by the mid-90s U.S. FCC decision to require mobile phone service providers to locate emergency (E911) callers with an accuracy requirement (October 1999 revision) of 100 m (67%) or 300 m (95%) for network- based solutions and 50 m (67%) or 150 m (95%) for handset-based solutions, the latter being the case with the use of GPS. The most promising technologies to achieve this on a continental level were cellular phone network-based TDOA methods and GPS if the latter could be made to operate under attenuated signal conditions such as urban canyons, forested areas and indoors. Attenuated signal environments are now often simply labelled “indoor” environments for the sake of simplicity. Early developments and testing of cellular phone network-based TDOA methods resulted in promising results with the use of GPS to precisely time synchronize signal transmissions (e.g. Klukas et al 1997, 1998). However, the additional cell equipment required proved to be a challenge. In addition, TDOA being an hyperbolic location method (similar to Loran- C for instance), observability was found to be low in a urban environment given the rapidly changing geometry of the available cells. Outside of urban areas, the cell geometry was simply not present to meet availability requirements. In parallel to the above developments, experiments to increase the integration time to potentially allow GPS signal reception under attenuated signal environments yielded promising results, especially with the use of assisted methods (Petersen et al 1997, Moeglein & Krasner 1998, Garin et al 1999). Given the existing space-based infrastructure and coverage advantages of GPS that makes possible an in-mobile phone solution, R&D efforts on improving GPS performance intensified rapidly. It soon became obvious that continuous outdoor and indoor location availability could be used in a large number of applications such as personal digital assistant location, asset tracking, vehicular navigation, and no doubt many others to be discovered, in addition to emergency services. These applications now form part of a location-based services business that is expected to grow from USD 0.5 B in 2003 to USD 28 B in 2008. One of the most important technical questions arising is what are the performance levels users want. Standard location and navigation performance parameters are important, namely availability, accuracy, reliability and integrity, and