Galileo is the European Global Navigation Satellite System (GNSS) designed to be interoperable with the United States' Global Positioning System (GPS). Galileo and GPS interoperability means that hybrid GPS/Galileo receivers will offer improved performance in several ways compared to GPS- or Galileo-only receivers. This paper presents the design and implementation of a software GPS/Galileo receiver, together with testing results using a real Galileo signal from GIOVE-A, the first Galileo in-orbit validation satellite. Furthermore, a new navigation solution algorithm to estimate the GPS-Galileo system time difference is proposed. Hybrid navigation results show that 2 m (2drms) positioning accuracy can be achievable without knowing the exact system time difference.
