The COMPASS Location System

The aim of COMPASS (short for COMmon Positioning Architecture for Several Sensors) is to realize a location infrastructure which can make use of a multitude of dierent sensors and combine their output in a meaningful way to produce a so called Probability Distri- bution Function (PDF) that describes the location of a user or device as coordinates and corresponding location probabilities. Furthermore, COMPASS includes a so called translator service, i.e. a build-in compo- nent that translates PDFs (or coordinates) to meaningful location identi- fiers like building names and/or room numbers. This paper gives a short overview on the goals and abilities of COMPASS. 1 Motivation There are a lot of situations in mobile computing where mobile nodes need to determine their current position. Ubiquitous computing applications derive context information from this position, e.g. in order to determine whether a user is currently at home, at work or on the way in between. Location-aided routing protocols for ad-hoc networks need position information to support their routing decisions. Navigation systems naturally rely on precise position information to plan the further route of a car or pedestrian. To support this large demand that applications have for precise location information, a number of commercial and research projects are working on this subject. Section 2 gives an overview on some of these activities. We have identified two major challenges that are not completely resolved yet: 1. Location information from multiple sensors needs to be combined eectively in order to present one and only one position to the application. Any single location sensor has drawbacks, e.g. is usually not available inside buildings, RFID sensors or WLAN/Bluetooth APs are only available where installed etc. So in order to provide reliable and pervasive location support, an ar- chitecture must use multiple sensors, combine their results and present this to the application. The application should not need to worry about what sensor(s) were used for the current position information. Additionally com- bining the results from multiple sensors may improve the precision of overall results. 2. Raw coordinates may not really be useful to an application that needs to know the position in terms of buildings, rooms, street names etc. So a lo- cation system should include an infrastructure to resolve the raw position information to some kind of symbolic position.