ABSTRACT
Obtaining the position of the end user’s device is fundamental to Location Based Information Systems and Location-Based Services. This chapter describes the most important positioning techniques available to localize end devices in outdoor and indoor environments, with emphasis on the former. The Global Positioning System (GPS) is perhaps the most widely used and ubiquitous system to obtain users’ positions. It is a complex and expensive system made of three major segments: the Space Segment, the Control Segment, and the User Segment. These three segments together enable GPS receivers to determine their location, speed, direction, and time. GPS satellites continuously broadcast a 1500-bit-long Navigation Message. The message is broken down into five subframes 300 bits long, and each subframe is divided into ten words 30 bit long each. Lateration is the process of calculating the user’s position using distances between entities.
