The novel concept of a direct radio frequency (RF) sampling receiver front end was analyzed, experimentally tested, and compared with a traditional superheterodyne front end that uses mixing to downconvert the signal before sampling. This study's goal was to demonstrate that signal power and phase are not adversely influenced by the use of direct RF sampling. The direct RF sampling strategy examined in this work uses sampling rates that are much lower than the carrier frequency but more than twice the signal bandwidth. Such a system employs a bandpass filter in front of the analog-to-digital converter (ADC) to avoid sensitivity loss via aliasing of out-of-band noise and interfering signals. This design approach was evaluated analytically to determine the effects of sample clock jitter, and experimental results using GPS signals were used to confirm the analytical results. The results indicate that direct RF sampling yields performance equivalent to that of superheterodyne mixing

The new direct RF sampling GNSS receiver front concept has been analyzed, experimentally tested, simulated, and compared to a traditional superheterodyne front end that uses mixing to down-convert the signal before sampling. The goal of this study has been to demonstrate that signal power and carrier tracking are not adversely influenced by the use of direct RF sampling. The direct RF sampling strategy that has been examined uses sampling rates that are much lower than the carrier frequency but that are more than twice the information bandwidth. Such a system employs a bandpass filter in front of the analog-todigital converter to avoid sensitivity loss via aliasing of out-of-band noise and interfering signals. This design approach has been evaluated analytically to determine the effects of sample clock jitter, and experimental and simulation results have been used to confirm the analytical results. The experiments have used computer data acquisition systems to record the outputs of direct RF sampling front ends that were connected to roof-top patch antennas. The results indicate that direct RF sampling yields equivalent performance to superheterodyne mixing if sample timing jitter is kept below well defined limits.

The future satellite positioning/navigation systems (i.e. GPS and Galileo) will provide civil signals on multiple frequencies, similar to those currently available for military purposes only. This paper presents a direct RF sampling front end design well suited for multiple frequency satellite navigation receiver design. No frequency downconversion is necessary; rather the particular frequency bands of interest are intentionally aliased using a wide band analog-to-digital converter (ADC). The resulting samples are passed to the memory space of a host PC for storage, and are saved to disk for eventual processing of the multiple frequency transmissions. The present paper describes the design of the front-end, validates its concept with collected data, and discusses the variations on the design of a generic multiple frequency GPS front end. Methods for processing the data obtained by the front end design are also presented.

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.

The future satellite positioning/navigation systems (both GPS and Galileo) will provide civil signals on multiple frequencies, similar to that currently available only for military use. The multiple distinct frequencies will provide many advantages to users of the navigation systems. This paper presents a direct RF sampling front end design well suited for multiple frequency satellite navigation receiver design. No frequency down conversion is necessary, rather the particular frequency bands of interest are intentionally aliased using a wide band ADC. The resulting samples are passed, via a doubling buffering FPGA design, to the memory space of a host PC for storage as well as eventually processing of the multiple frequency transmissions. This paper describes the design of the front-end, validates its concept with collected data, and discusses the variations on the design of a generic multiple frequency GPS front end.

A fully software Global Navigation Satellite System (GNSS) receiver implementation holds many advantages over traditional receiver designs. The most significant of these advantages is the tremendous flexibility in the signal processing. One of the difficulties associated with a software radio implementation is programmable processing power required. Typically a chip specifically design for a single task, such as an application specific circuit (ASIC) can provide much higher throughput for the specific task it is hardwired to perform. However with the currently technology a fully functional multi-channel real time GPS receiver is feasible. This has been proven with a PC platform as well as in a DSP implementation. In the first part of the PC implementations is described. The main focus of this paper is an application of the software radio critical for developers of GNSS (current GPS and future Galileo) receivers - the evaluation of various front end ASICs for use in GNSS receivers. Is has been relatively easy to compare different GPS receiver architectures. However, for those developers looking to use individual components, consider the front end ASIC individually as an example, it is quite difficult to quantify the performance of various commercial versions available using traditional receivers. This not the case with software radio since the software architecture is independent of the front end design. Results of testing four different front ends are reported within the paper.