Sect_1.1.1

1.1.1 Designing a Satellite Positioning System

INTRODUCTORY REMARKS

In order to appreciate why the NAVSTAR Global Positioning System (GPS) is configured the way it is, and how it satisfies the needs of a variety of users, it is necessary to understand something of the basic concepts and technological aspects of a satellite-based positioning system. As an exercise, some general objectives for designers of a hypothetical satellite positioning system can be identified. For example:

To devise a system of positioning based on control stations in near-earth orbit, rather than on a conventional network of ground control, that would satisfy the positioning requirements of both stationary and moving platforms.
To study various satellite positioning design scenarios, and their impact on both the system operators and the users.
To investigate the technological aspects of such a system, as they relate to satisfying both moderate and high accuracy requirements.
Where technological requirements are not entirely met, to devise operational and/or computational strategies that can overcome these deficiencies.

An additional objective may be included:

To identify those elements of the GPS system which have parallels with the hypothetical satellite positioning system referred to above.

The approach used in this text is to work through the design process in a logical manner, introducing new elements as required, and to try to identify the significance, advantages, problems and impacts of each new system element.

The premises underlying this design process are:

That satellite positioning technology is worth developing, in order to satisfy a range of navigation and surveying applications.
That the process can be understood from the viewpoint of conventional notions of positioning.
That the design of any satellite positioning system is a compromise process between often unreconcilable issues such as economical considerations, technological barriers, and political imperatives.

The aim is, in effect, to "demystify" GPS, by first ensuring that an understanding of the principles upon which GPS is based are grasped, and then gain an appreciation of both the limitations of the system and its potential for accommodating innovative positioning strategies.

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