The software radio has been described as the most significant evolution in receiver design since the development of the superheterodyne concept in 1918. The software radio design philosophy is to position an analog-to-digital converter (ADC) as close to the antenna as possible and then process the samples using a combination of software and a programmable microprocessor. There are a number of important advantages to be gained through full exploitation of the software radio concept. The most notable include: 1) The removal of analog signal processing components and their associated nonlinear, temperature-based, and age-based performance characteristics. 2) A single antenna/front-end configuration can be used to receive and demodulate a variety of radio frequency (RF) transmissions. 3) The software radio provides the ultimate simulation/testing environment.
Global Navigation Satellite Systems (GNSSs) are the latest and most complex radionavigation systems in widespread use. The United States' Global Positioning System (GPS) and, to a lesser extent, the Russian Global Orbiting Navigation Satellite System (GLONASS) are being targeted for use as next generation aviation navigation systems. As a result, it is critical that a GNSS achieve the reliability and integrity necessary for use within the aerospace system. The receiver design is a key element in achieving the high standards required.
This work presents the complete development of a GNSS software radio. A GNSS receiver front end has been constructed, based on the software radio design goals, and has been evaluated against the traditional design. Trade-offs associated with each implementation are presented along with experimental results. Novel bandpass sampling front end designs have been proposed, implemented and tested for the processing of multiple GNSS transmissions. Finally, every aspect of GNSS signal processing has been implemented in software from the necessary spread spectrum acquisition algorithms to those required for a position solution.
The GNSS software radio is the first of its kind and will thus bring all the assets associated with the concept into GNSS receiver research. Not only does the work describe the multiple benefits available through a GNSS software radio implementation, but it also establishes the feasibility of such through actual hardware design and experimental results.