The continuous developments of software-defined radio technology resulted in the
appearance of the first real-time GPS software radios at the beginning of this century.
For the first time, it was possible to realize a complete GNSS receiver without
going into the depths of cumbersome hardware development that requires development
or programming of low-level digital circuitry. The hardware development efforts
were indeed so high that only a very limited number of companies or research
institutes could afford them. Furthermore, the implementation constraints were so
severe, especially for the first generation of GPS receivers, that often crude signalprocessing
approximations were necessary to allow a real implementation. Currently,
software-defined radio technology not only allows receiver implementations
by a larger research community, but also drastically increases the signal-processing
capabilities. It also has the potential to become, in certain navigation areas, a commercial
success