We discuss GPS receiver architectures based on software defined radio techniques. The reason for doing this is to obtain a reconfigurable receiver with a wide range of applications. There is a need for a unified platform that will allow receiver development and testing for various applications; this speeds the design process and reduces the costs. With the current functionality of the GPS constellation and the promise of the complete Galileo constellation, efforts have been focused on the 1575.42MHz L1 signals for the software receiver implementation. These single frequency navigation signals, particularly when coupled with space based augmentation such as WAAS or EGNOS are likely to fulfill the navigation needs of most users. In order to develop and test the software algorithms, a complete L1-band antenna and RF front-end has been designed capable of processing the wider bandwidth necessary for the Galileo L1 BOC(1,1) signal. This front end provides digital samples to the host computer for the software receiver implementation. In addition, a GNSS signal generator was designed and implemented in Simulink to be used for algorithm development and testing to offer the user the option of using the front-end to collect and process actual GPS data or generate simulated GPS signals. The GPS software receiver was implemented in Matlab and is capable of performing GPS satellite acquisition and tracking on both real GPS data and simulated GPS data with extreme properties. A complete GNSS software receiver was implemented and the receiver is able to perform acquisition, code and carrier tracking, navigation bit extraction, navigation data decoding, pseudorange calculations, and position calculations. We have created a pedagogical tool for the GPS newcomer: A front-end which obtains actual GPS data via the USB port, a complete Matlab implementation that provides a real-time GPS and Galileo (as defined by the current ICD) software receiver, and finally a textbook, Borre et al. (2006), that describes the whole thing.
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