Software-defined radios (SDRs) have been around for more than a decade. The

first complete Global Positioning System (GPS) implementation was described

by Dennis Akos in 1997. Since then several research groups have presented their

contributions.We therefore find it timely to publish an up-to-date text on the subject

and at the same time include Galileo, the forthcoming European satellitebased

navigation system. Both GPS and Galileo belong to the category of Global

Navigation Satellite Systems (GNSS)