Ch 2. Fundamentals of Satellite-Based Navigation and Timing

John W. Betz

Chapter Overview:

Satellite-based navigation and timing (satnav) has become the predominant technology for positioning and timing, with billions of users and an almost infinite number of applications. As additional satnav systems are added to the Global Navigation Satellite System (GNSS), this trend will increase, even while other technologies are increasingly used to augment and extend satnav to overcome its limitations.

Section 2.2 introduces satnav basics – the measurements; calculations of PVT; and the overall structure of a satnav system. Sections 2.3 through 2.6 describe different parts of a satnav system: the space segment, navigation signals, the ground segment, and the user segment respectively. An increasingly important part of satnav is its augmentation systems of various types, discussed in Section 2.7. Key to satnav performance is understanding, characterizing, and mitigating various sources of errors; this topic is discussed in Section 2.8. Section 2.9 summarizes this chapter.

While the principles of satnav are straightforward, sophisticated implementations are needed to provide the exquisite performance that is commonly obtained. The unique capabilities and benefits of satnav now touch virtually everyone on Earth. The principles and techniques summarized in this chapter, primarily developed either by or for GPS, are now being applied and extended to a GNSS that will consist of four global satnav systems, three regional satnav systems, and a growing number of SBASs whose coverage will continue to increase over much of Earth’s landmasses. The projected set of signals transmitted by the GNSS occupy much of the L-band spectrum between 1 GHz and 2 GHz, as well as a slice of the S band between 2583 MHz and 2500 MHz, as shown in Figure 2.13. This rich set of signals, to be transmitted by as many as 150 satellites, promises a new revolution in satnav.

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