On GPS receiver architectures

Abstract: Navigation can be described as the art of finding the way from one location to another. Clearly navigation is something that we perform in our every day lives and the role of navigation can not be underestimated. There exist many technologies that implement various navigation systems to aid in this process. The most popular navigation system is the Global Positioning System (GPS) owned and operated by the United States of America Government. GPS is a space-based radio navigation system. Initially GPS was primarily intended for military use but the civilian community has found increasing use of GPS. The main reasons why GPS has become such a success is that users anywhere in the world can obtain accurate position, velocity and time measurements free of charge. GPS receivers have significantly come down in price since the inception of the system and today can be considered inexpensive – as little as 1000 SEK or 125 € for a 12 channel hand held unit. The civilian use of GPS is expected increase even further and new applications of GPS will emerge. GPS is targeted for a modernization process where new civilian signals will be added to provide more accurate and reliable measurements. The European Union is planning a new space-based navigation system, Galileo, which when operational will provide the civilian community with an alternative or complement to GPS. It is of great interest to develop flexible GPS receivers that can easily be adapted to new applications and various user scenarios. New receivers must also be developed for the modernized GPS and the upcoming Galileo system. Another area of navigation interest is the integration of GPS and inertial sensor measurements. Inertial sensors can be found in another type of navigation system, namely Inertial Navigation System (INS). Integration of GPS and INS provide a more reliable and accurate navigation system. The evolution of low cost Micro Micro Electro Mechanical Systems (MEMS) inertial sensors has dramatically decreased the cost of INS. Hence applications of integrated GPS/INS systems will find new markets that have not been considered before because of the high cost associated with inertial sensors. In this thesis Programmable Logic Devices (PLDs) are used in combination with GPS software receivers. This has enabled the rapid development of flexible GPS architectures ideal for adaptation to various user scenarios and applications. It is also show that this combination of PLDs and software can provide a prototyping environment for inclusion of new GPS or Galileo signals with great flexibility. Furthermore a platform for the integration of GPS/INS is proposed. The main idea is that data processing should be implemented in a single processor. This alleviates one obstacle commonly found in other GPS/INS integration implementations, which is the limited observability of measurements from both GPS and INS. With the new platform full observability of all measurements is obtained. The proposed platform also provides synchronization of GPS and INS data streams at the lowest possible level. Exact synchronization of measurements is essential to provide an accurate implementation of data fusion algorithms.