Chapter 3 detailed the fundamental techniques used in positioning. In this chapter, we review several examples of existing positioning systems that use these techniques. In particular, we focus on wireless positioning systems to motivate wireless local area network positioning. We discuss the Global Positioning System (Section 4.1) and cellular positioning (Section 4.2) as examples of positioning systems used in outdoor environments, and positioning based on ultrasound and infrared (Section 4.3) as examples of indoor positioning systems. We then proceed to motivate and describe positioning systems employing wireless local area networks (Section 4.4). Finally, we conclude the chapter by comparing the advantages offered by each system.

The Global Positioning System

Historical perspective

In 1957, the first artificial satellite known as Sputnik I was launched into the earth's orbit by the Soviet Union. Within days of the launch, scientists at Johns Hopkins University noted that they could determine the position of the satellite based on the Doppler shift associated with its radio transmissions. What was even more interesting was that if the position of the satellite were known, this Doppler shift could be used to determine the position of a satellite receiver on earth. This observation ushered in the development of global navigation satellite systems (GNSS).

The first operational satellite-based positioning system was Transit, also known as the Navy Navigation Satellite System (NAVSAT). This system was primarily used for military operations by the United States Navy.